Undisputed World Champion of MMA

[Cross_Trainer]

This is a little along the lines of my other post, but deals with a more plausible scenario rather than hypotheticals (fun as hypotheticals may be)

If a fighter won belts in the same/very similar weight class in both the UFC and Pride under both of their rules (Pride's in Japan, UFC's in America), would they be considered for all intents and purposes the unified world champion, since they won in the 2 major organizations under both rulesets? Or are the other organizations out there important enough that it would still be disputed?

Also:
1. What do you think that would do for MMA in general? I would suspect that it would improve its popularity, especially if the winner is charismatic and a heavyweight. People seem to enjoy a sport more when there's a top person to identify it with.
2. Is it possible and/or likely in the near future? It seems that Pride's fighters have a lot more money and little to gain by going into the financially poorer UFC. I'm also not sure how much the two organizations think of each others' legitimacy.
3. Is there anyone who could pull it off at any weight class, and keep both titles for a long period of time (They'd have to fight more often than normal, though...)
4. Any other thoughts on this that I haven't addressed?

Thank you for your time.