SUGGESTION
Allow for import/export of full teams and/or systems from one universe to another.
REASON
This would allow for three things. One would be a 'World Championship/WBC' scenario (or whatever tournament-style flex you wanted, within the scheduling limits). The other would be some great opportunities for users to swap teams for fun to see which team is 'best'. And finally, it would allow for multiple online leagues to form a rough confederation once per season/year/whatever time frame to do a 'best of best' series.
The possibilities are far reaching, and it would make the online world incredibly flexible (and realistic - what if a team leaves one league for another?
), as well make single-player scenarios far more robust and creative.
PRIORITY
High for me. I've skipped this year's version despite the fact that it looks much nicer. I'm waiting for a more flexible 'world baseball' scenario through either means similar to that which I've suggested (if that's feasible) or a combo of what others have said (MogulChamp, etc.). I'm a 'lifer' if that kind of flexibility arises in the game. Thanks for reading.