The Ultimate Universe is not obsolete so long as the issues still sell within the Top 35, which they all do (and some usually better). Mark Millar said it best once, that so long as Marvel can sell Avengers and Ultimates within the same month, the Ultimate Universe will churn on.
It is a fair point that after some 6-7 years, the Ultimate Universe has become what it was supposedly set out to be opposed to. It now has it's own rigorous continuity, although less of it (7 years vs. 40 is no contest). In half of it's titles, the A-List creative teams have left for greener pastures (UFF, UXM), and in USM, Bendis is running out of steam after 100+ issues and is too arrogant to admit it (plus, as the issues are still selling within the Top 10-20, management isn't going to muck with it). A universe that professed to have a contained universe now has a spin-off franchise (MARVEL ZOMBIES spun out of UFF, mind you) and averages one crossover "event" mini a year, and many of those mini's have been disposable and resulted in less fallout in the core titles than many of 616's events (love or hate CW, it has effected every book down the line, but read the core Ultimate titles and you'd hardly know they all fought a giant alien recently). Plus, Ultimate prided itself on being "new", but something that is over half a decade old just ain't "new" anymore. While there are far fewer trades to catch up on older Ultimate stories than for 616, a new fan coming in would be almost as lost hopping aboard a random Ultimate issue as they would 616.
Throw in the fact that lateness has become an issue (ULTIMATES 2 has drug on a half year longer than Marvel expected in 2006, and ULTIMATE WOLVERINE VS. HULK has obviously become the new DAREDEVIL: TARGET even if Marvel won't admit it), and that Marvel's editorial board has committed itself to energizing 616, and you get the feeling that Ultimate has become the sidekick. It is there because it sells, and because writers have more creative freedom. I would argue that many of the writers who "made their name" at Marvel in Ultimate, at least at the beginning, have been writers who by nature tend to bulldoze over continuity anyway, such as Bendis, Millar, and Ellis. Ultimate trained them into getting more of their way with characters and shifting onto 616 where they have 40 years of backstory to conform too hasn't always worked out for them, to be modest.
On the positive side, Ultimate has provided ore for Marvel's multi-media department when they want video games and movies with more "modern" spins on origins. It gives a movie or video game studio an option for an update that doesn't come from them, such as switching from "radioactive spider" to "genetic super-spider" without having the fans cry out. Of course, this has as many strengths as it does weaknesses as Ultimate, like 616, has had plenty of blunders. As good as Millar's UFF was, giving Dr. Doom superpowers just seems to take something away, like if Batman got superpowers. Ultimate Goblin is simply a clone of Hulk and I am glad Raimi skipped it. But, it provided ore for well-recieved DTV's and video games, least in terms of sales. And it has provided those alternate media sources with alternate designs without having to do their own. I'd trust Hitch with a new Thor design than, say, in-house Activision artists.
Should Ultimate have a finite end? Of course, or at least some progression (like having Spidey move up some grades), otherwise it will feel more like "Neverland" than even 616 or ARCHIE. But, mainstream comics just don't "end" universe lines, at least so long as they are selling. Endings only come when they are abruptly shoehorned in as sales lag, much like, say, NEW UNIVERSE or 2099. So long as Marvel can sell ASM and USM with respectable numbers, they will. It would be naive, though, to see that Ultimate has in a way become a victim of itself. But Joe Q's Marvel is a Marvel that denies any and all problems, so don't expect this to come up. So long as sales are good, any problem is ignored.
Quite frankly, what UFF and UXM need are A-List creative teams who have some sort of clear idea. Carey's UFF isn't bad, but coming off of A-Listers like Bendis, Ellis, and Millar and you will lose steam. And while I adore Kirkman's other work, his run on UXM is rather weak as he seems to not have much focus. Ironically he would be a better fit on USM, a title Bendis doesn't seem to want to relinquish over his dead body, despite the fact that it argueably hit a creative lull around ULTIMATE CARNAGE and ever since was hit or miss, with the last "miss" being the last I could bare (Ultimate Clone Saga, the longest storyarc in the title that repeated all of the 616's clone bungles in 1/3rd of the time, even with the benefit of hindsight). Plus, after 6-7 years, all the "Ultimate" versions of key characters have been done and so one is left scraping the bottom of the barrel, like for Diablo or Ringer. The Ultimate universe has provided few "original" characters on it's own and those that have emerged usually stunk, like Geldoff or Hawk-Owl. ULTIMATES needs to ship on time and USM needs new blood, but it has to be A-List blood. Bendis needs a break from that, because it has ceased to be innovative and has delved into obsessive fan-fiction (plus, how is a Spider-Man universe where his ENTIRE supporting cast knows his identity ANY different than 616, beyond age?).
The Ultimate Universe isn't obsolete, and isn't going anywhere anytime soon. It does need a few check-up's though, but I doubt they are coming. Rather than being seen as "the line of the future" anymore, they're seen as just another bunch of decent selling Marvel books, where creative teams come and go.