Big fat monolithic upgrades for iOS should come to an end. And the faster, the better. Here is why.

1. iOS users are very engaged with their devices. They buy more apps, they use more of them, they surf the web more often and choose to upgrade their device to the latest iOS release more easily than any other mobile platforms. Apple should take advantage of that. Right now, they don’t. Users have to wait a very long time in order to see improvements to their device. How is this different compared to Android devices that are never upgraded because of their mobile operators? At the end of the day, this is pretty much the same thing. Since the vast majority of iOS users are quikcly adopting new iOS releases, Apple should not fear of any ecosystem fragmentation. 
2. Apple should seperate releases of the base OS from the builtin apps. I know Apple wants to package an iOS device with a bunch of apps that will form the whole user experience and set expectations. They can still make these apps mandatory via the App Store. After an iOS upgrade, a process to download the new set of basic apps could be started right away to complete the upgrade process. The new process would allow Apple to push specific updates to fix things or improves the feature set. Remember the original iPod touch which came out and was missing many of the iPhone stock apps? Later Apple offered a paid upgrade to iOS in order to bring many apps to the iPod touch (Mail was one of them).
3. Apple puts a lot of pressure onto itself by offering only big upgrades. They must put everybody on the same schedule or release cycle. But we all know that not all features of iOS requires the same upgrade cycles. Market is rapidly changing and forces new priorities to everybody, including Apple. By sticking to a yearly upgrade cycle, iOS users are sort of penalized.
4. There are less and less low hanging fruits in the tree. iOS is a mature operating system. What is left is more refinements and this is exacly what lighter operating system releases is all about. Remember iOS 6.1 ? Or iOS 5.1 ? As the core operating system matures, with OTA incremental updates, it is more easier than ever to push more specific feature upgrades to the users.
5. More and more apps are created because of the lack of basic and often requested features in Apple’s core applications. These new or updated features a hard to come by from Apple so this creates a window of oppurtunity for others. How many mail clients does the App Store offers?

As you can see, time has come for Apple to split their iOS releases between the base operating system and core applications. iOS 7 expected refreshed look and feel could be the last of such big upgrade.

Here is a commented version of Justin Williams wish list for iOS 7 and WWDC.

1. A completely refreshed design language for iOS 7 that sheds the Forstall and oozes Ive. [This one is a must. I think Apple had enough time to imagine one since the management shake up last fall that put Jony Ive in charge or Human Interaction Group].
2. Modernized and updated system apps for iOS that match the new Ivey design language. [Obviously].
3. A services/sharing architecture on par with what is offered by Windows Phone and Android. [This one is rumored since a long time like XPC communication.]
4. An update to iMessage that makes it reliable. [The backend of iMessage i.e. iCloud is more the root cause of the problems IMHO].
5. An update to iMessage that allows people to leave group chats. [But group chats in iMessage aren’t really groups, they are a list of recipients on the device where the conversation started.]
6. Multiple people on FaceTime calls. [This one is really nice but I would expect it to be available on Wifi only or LTE networks.]
7. Xcode 5 with better refactoring tools, smarter smart sense and less crashes. [Hey, this is WWDC, so some new stuff for our devs too!]
8. A separate documentation viewer from Xcode itself so that command-tabbing between code and documents is possible and I can remove that weird purple icon DashCode uses from my Dock. [Yep!]
9. Transitioning the beta testing process from device limits and towards Apple ID’s so anyone with a targeted ID can install a beta product on any device they own. [Apple will impose a limit somehow on this like 100 Apple IDs.]
10. The ability to distribute betas over the App Store. [Bye bye TestFlightApp?]
11. Analytics tools for App Store developers so we can see where referrals and sales funnel in from. [This one is such a missing piece in iTunes. Analytics are the basis of many marketing decisions so I wonder why Apple doesn’t provide them for the developer community.]
12. Real-time sales analytics. It’s 2013. Next day sales charts just won’t do. [See 11]
13. The ability to finally, once and for all delete old app IDs from the portal. [At least, to hide them from the portal day-to-day operations.]
14. The death of the provisioning profile to make deploying to devices less of a headache. [Not sure this could happen.]
15. The removal of the 100 device limit for iOS beta testing, or at a minimum deleting a device gives the slot back to you before your iOS developer program renewal date. [There could be a limit on how many device removable you can do within a subscription period. This would be better.]
16. A faster, more reliable iCloud. [Agreed]
17. An updated iCloud that obviates the need for services like Dropbox. [A must that should be coupled with a Files.app application on iOS.]
18. Syncing with Core Data and iCloud to actually work so that we can stop writing blog posts about it.
19. A backend service that ties to iCloud that enables Apple platform developers to deploy a web service to tie their apps together. Think Google App Engine, but with a flat UI designed by Jony Ive. [Yep, this one too is kind of a must.]
20. The ability to customize the lock screen on iOS. [In what way?]
21. The ability to organize your springboard free-form. [To make sure it becomes a mess? Nope.]
22. The ability to add widgets to your home screen. [Fuck the widgets, this is a retarded concept. Apps. Apps. Apps.]
23. Quick access to key service toggles like Airplane Mode and Bluetooth. [Sure.]
24. A more reliable Game Center so Loren doesn’t break it again.
25. The ability to Find My Friends without having to open up an app covered in leather. This will allow vegetarians to finally use the product.
26. Updates to iTunes Match make it more like Rdio and less like an unreliable mess. [iTunes Match is working great for me.]
27. An updated notification center that supports swiping away notifications
28. An updated notification center that supports quick actions from a notification [Like? Which actions?]
29. An updated notification center that offers Game Center achivements for successfully tapping the tiny “X” on the first try.
30. The ability to download Mac apps from your iPhone or iPad and have them show up on your Mac when you get home.
31. The ability to download iPad apps from your iPhone and have them show up on supported devices automatically. [Interesting idea].
32. A web-based front-end to iTunes that doesn’t involve ever launching iTunes again. [Could be easy to do since iTunes.app IS a web browser anyway.]
33. Selective backup restoration from an iCloud backup. [God, yes!]
34. Read and write access to Photo Streams. [From an app perspective I guess, yes.]
35. The ability to set new default apps for things like the camera, calendar and browser. [Yep, and they started to do something quite like this is their Maps for pedestrian and bus transportation.]
36. Deeper integration for third-party services beyond just Twitter and Facebook. [YES!!!]
37. The return of Google Maps. [Just head to the App Store and download it.]
38. A Q&A session with Tim Cook at the conclusion of the Keynote where he answers questions from anyone not named Robert Scoble.
39. The ability to update apps in the background without weird geofencing hacks to accomplish it.
40. A new App Store app that isn’t a complete turd. [Oh, you don’t like the App Store app on your iDevice?]
41. An update to OS X that is not only stable and fast, but incorporates new features both pulled back from iOS and to further push it ahead of Windows 8.
42. The ability to disable that god damned Mac App Store updates notification without having to actually update or open the Mac App Store. [Yep!]
43. Port UIKit back to OS X so that I can stop reading tweets from people bitching about how old and dated AppKit is. [Not going to happen.]
44. Retina screens for every Mac.
45. A new Mac Pro. Finally.
46. Air Drop support across the Internet and not just your local network. [Should come with the new iCloud services competing Dropbox.]
47. Pull all the Google-centric code from WebKit 2 and make the next version of Safari suck less. No more reloading all my tabs please.
48. The ability to read your iBooks on your Mac.
49. MapKit for OS X.
50. Siri support for the Mac.

(Source: carpeaqua.com)