1) The Reaper War: This RP would take place during Mass Effect 3, but with a twist: Shepard died when the Collector base was destroyed. Characters would then have to try and fill his shoes and unite the galactic powers against the Reapers while not getting killed in the process.
2) Rise of the Yahg: This RP would take place several years after the Reaper War after many of the Mass Relays had been repaired. Basically, the Yahg would've reverse engineered the spacecraft used by the First Contact team that they massacred and used that technology to build an invasion fleet. Lacking a Relay, they'd use their FTL drives to get to the nearest system, which, while a good deal slower, would also leave them with the element of surprise. After a long journey, the Yahg fleet would launch an attack an unsuspecting colony, which would just manage to get out a vague distress signal before going silent. Characters would be tasked with defending the colony against the Yahg attack.
Edit: Here's another idea for a possible Mass Effect RP:
3) The Prothean Treasure: Around one month after the Battle of the Citadel, the Galaxy was shocked to discover that the valiant Commander Shepard was believed to have been killed when the SSV Normandy was destroyed. These (greatly exaggerated) reports of the Commander's death overshadowed a discovery made in another corner of the Galaxy: a partially intact Prothean VI which dispensed information on a Prothean cache of unimaginable proportions. According to the data recovered from the VI, the cache is believed to contain Prothean weapons, technology, priceless Prothean cultural artifacts and precious minerals galore. However, the VI was too damaged to give the exact location of this "treasure," and the research team which discovered the VI was only able to recover a few data fragments which provided clues to the cache's location. The research team spent over a year putting the pieces together to try and narrow down the cache's location. Unfortunately, they discovered that the most likely location was somewhere in the Terminus Systems, an area where human colonies were reportedly disappearing. Despite the danger, a few of the researchers decided to try to go to the Terminus Systems on their own to find the cache: they were never heard from again. The other researchers had a falling out and went their separate ways, with each trying to find their own way to locate the treasure which now consumed them. Some sought help from their governments, some made deals with mercenaries, others tried to make deals with... less reputable characters.
Now the race is on to be the first to find the treasure. Whether seeking it to help one's people, out of an academic fascination, or due to good old fashioned greed, numerous ships are now braving the unknown perils of the Terminus Systems in hopes of finding the cache for themselves before it's too late...
Alternatively, if folks are getting tired of plain old Mass Effect character RPs, I'm also considering doing a crossover. Anyway, that's all that comes to my mind. If you have any ideas for an RP, or any suggestions to improve on my ideas, please feel free to share
OOC: viewtopic.php?f=31&t=343770
Yes, the major events would still happen (barring some catastrophic failure at least)