I would call for 5 three min rounds and championship fights 9 three min rounds.
I'd be happy with a compromise of a 4 minute round x 3 rounds for non-title fights, and 4 minutes round x 5 rounds for title fights.
Only problem with 9 rounds at 3 minutes each, is that's 27 minutes, and I think the Unified Rules limits the fight to a grand total of 25 minutes. That means that they would go with 7 rounds instead. Personally I think most fighters can handle five minute rounds pretty well, with two general exceptions - Heavyweights, and cards at high elevation (Denver, Mexico City, ect.) The fact that they put the Heavyweight belt on the line in Mexico City is easily one of the dumber things I've seen. Same thing with having a title fight in Dubai, where it was apparently blazing hot in the arena.
I think the main advantage of having 4 minute rounds over 5 minute rounds, is the fighters will have more energy, especially in title fights, with Heavys, and when at high altitude. And I think the main advantage of 4 minutes rounds over 3 minute rounds, is there is less down time (break time between rounds.)
Another HUGE advantage of 4 minute rounds is that a most fights will be a max of 12 minutes. And remember how I said the Unified Rules limit a fighter's activity in a night to 25 minutes? Well a fighter could have two non-title fights (2 fights at a max of 12 minutes each = 24 minutes) in a single night. This would mean mini-tournaments could be held on occasion.
Overall I don't think they need major changes to the round times, it just would be nice in some ways. I think a lot of wrestlers and BJJ guys would balk at the notion of 3 minute rounds, and I can't blame them. It's a 40% reduction in time for them to work in any given round.
I've spent too much time thinking on this obviously. The UFC isn't going to change shit to their cookie cutter product.