That would be great!
I mean, I'm by no means a fan of the UU, but I really enjoyed the crossover.
I hope for more crossovers that not only concern Spidey, for example a crossover of the X-Men-Teams, and a meeting of the Avengers and the Ultimates.
You are missing the prime Avengers fan rule, Torture and Genocide are OK if Cap approves, Feeding the Starving is evil if Cap doesn't aprove.
Marvel Now! has been Marvel testing the waters for a reboot. I bet "Spider-men 2" will be the catalyst for the Regular Marvel U. and the Ultimate Marvel U. merging and reshaping reality and rebooting continuity. Other than that, I can see no reason to do it. Oh, except $$$. The first one wasn't that good and mixing the two universes (something I always thought they said they wouldn't do) only diminishes the Ultimate U. in the long run.