There are indeed some issues with regard to XI fitting into canon, even with all the work Abrams and co. have done as far as creating some kind of "plausibility" goes with Spock/Nero coming to "this" timeline from the "original timeline." I'm not sure how Star Trek: Countdown fits with either the "original" timeline of the new one, because it's odd how in the comic Nero sees the Shatner-Kirk and recognizes the Pine-Kirk in the film as if the latter were the same. But in any case, I don't think "Spock Prime" (as he's being called) came from the TNG/DS9/VGR/Nemesis/etc. timeline. He came from a slightly different one, where Pine was the Kirk he knew and the technology existed in the ways that the film displays. I mean, obviously the technology on the Kelvin was different from and perhaps more advanced than the technology we might expect from "The Cage" level TOS. The uniforms are different, the ship itself was different. Which means that Spock Prime, while apparently "our" Spock, was really from a third timeline, one consistent with the new film up until (and beyond) the point where the Narada destroys the Kelvin. Does this make sense? Perhaps I'm spending too much time worrying about it and should just enjoy the new film for what it is, a new Star Trek universe that tries not to ignore the old one.
Although a bunch of changes (timeline, in particular) can be explained away by Nero's incursion, it appears the recasting of the character isn't meant to represent an actual difference in appearance between the two Kirks, etc, but is artistic license. The dialogue in the film clearly establishes that the characters are supposed to look alike: Apart from Nero recognising Kirk, Spock also recognised him immediately, and Spock also identified Scotty. This has precedent : Saavik was recast and supposed to be the same person, for example.
I've suggested something similar, except that I don't accept the idea of timelines fracturing with a whole new one emerging while the original stays intact, only now its without the people who went back to the past, and will never have them again. The uniforms on the Kelvin were from a period we've never seen, so naturally they don't fit with THE CAGE. You were a little off on that one. I've thought about it, and they could be taken as an evolution from the Archer-era uniforms, moving towards what we know. How they'd become the CAGE uniforms at any future point...that sort of escapes me. The tech too is the main point where we agree. Kelvin looks too good. What I suspect is that this, like the Mirror Universe, is an alternate reality from "our" Star Trek. It has a lot that's similar, but it differs too. (For example, how did the Romulan-Vulcan connection come to light years before "Balance of Terror" should have happened?) This DIFFERENT reality has now been altered by Nero and Spock. Since the Countdown story seems to say THAT 24th century has remained intact, fine. Apparently the differences introduced by Nero (and older Spock?) aren't bad enough and have ironed themselves out so that by the 24th century, all's pretty much back on track. (Without Vulcan, I dunno how, but it apparently does happen.) I'm more and more leaning on the idea that JJ-Trek is NOT the original universe, but simply similar, now a little less so due to Nero. Still, MUCH is the same, and now the original characters are in their correct places, possibly for years to come. How will Piine look with a paunch?
Meh. They should have started completly over. Why bring all the baggage over from the old trek just to ignore it? I wuld have liked to see an adventure completely devoid of any specifi reference from established Trek and just have a good adventure.