if I were to guess I'd say KLP will likely move the whole UI the same direction all their apps seem to be going, which is grrreat. But I think there will be some OS level stuff, similar to project butter. Except this time having to do with battery life and the way the OS handles multiple running apps, things like that.
Of course it's all just rumours and speculation, but if it is indeed 4.2 straight to 5.0, it's likely to have a bunch of notable things. Jelly bean wasn't even that bad and that was only a .1 update.
until you see a picture of a phone running it, you know it's not coming for a long time. Always happens when a phone is testing an OS update, the pics come out showing the version number. So we'll see.
I say it will be like GB > ICS, i.e. fucking huge. To me JB just polished up ICS and made it usable. KLP looks like it will be a massive update
As for HTC, yes, there is no sign of 4.2.2 as yet, but again, with just a single phone requiring software support it won't be as bad as 2011/2012. I worry about Sony because of the sheer volume of phones they have committed to keeping up to date. As far as I know this is the list of currently supported models beyond 4.1.2:
Z, ZL, SP, L, T, TX, TL, V.
That's 8 SKUs and 4 different chipsets. I have heard Samsung have around 1500 developers working on OS updates atm, Sony have around half that amount and a similar number of SKUs being supported at any given time, so you see where the problems are.
Again, the list is only preliminary, I could easily all 2012 phones fall out of the list once they get 4.2.2, there will be a lot of complaints if the T family doesn't get 5.0 though.