Nexus/One/Silver devices should be upgraded for 2 years
Here's why - Google seems to be switching to one major release per year, like Apple. So they will be showing the preview at I/O, and actually release that version in fall.
I love this strategy because not only does it give time to OEMs to port the new version to their devices "at launch" (or very close to it, hopefully), but it also allows developers to support all the new APIs and design style and whatnot, like it usually happens on iOS. I've actually been asking them for a long time to do this, too. "Releasing" an Android version that only one or two devices can get doesn't make a lot of sense to me, when everyone else has to wait 6 months for it. If a lot more devices and people could get it at "launch", that would be a lot better.
The problem with this, however, is that let's say you bought a Nexus 5 with Kitkat. Then you will only receive the L update - and that's it! Because the M update would be coming in fall 2015, and the way Google does things now, it means you won't be getting anymore updates for Nexus 5. L will be the one and only major update for your phone (come on, 4.4.3 and 4.4.4 don't count).
That just doesn't feel right. If Apple can push 3 such updates for their devices, surely Google can push at least two? Otherwise they would be literally pushing 3x fewer updates than Apple.
I can forgive them if they don't push the L update to Nexus 4 and Nexus 7 2012 this time (then again I don't own either, so I imagine people owning them would be more upset than I am about it), but I won't forgive them if I buy a phone with L out of the box, and then I only receive ONE major update, making my phone supported essentially only a year, when the new version comes out.
So if they are going to push only one major update per year, then they need to support the Nexus/One/Silver/GPE and whatever such program they might have for 2 years, and give them 2 major updates, otherwise I think they are doing a huge disservice to their users, and I think everyone should be outraged about it and demand 2 major updates.