If I was given the opportunity to make a three part movie series or a new season, I'd choose the three-part movie series and I'd hire a bunch of the original writing staff, including David X. Cohen and Ken Keeler to write them for me - with the express intention that they should work as feature films (rather than episodes stuck together), they should work as a trilogy, containing a story arc, and the final one should provide closure for the series.
If you're asking people to come up with specific plot ideas, you should probably be posting in this section of the forum:
http://www.peelified.com/Futurama-Forum-6/Threads-0.html