It's possible, sure, but no plans set in stone. When Mass Effect began their vision was to make a trilogy about Commander Shepard and his ongoing crusade against the Reaper invasion. Beyond this we've had one exclusive non-Shepard game in the form of ME:Galaxy and the books. As a franchise it's still relatively focused on game sales.
Game sales don't guarantee heightened interest to revise original intentions and, given the collection of other brands, it's more likely Dragon Age may continue to prosper after ME3 is released.
The thing to keep open-minded over is the scope of what needs to be done in Mass Effect post-Shepard relies more on player incentive than developers working to the voice actors, the same familiar settings, and maintain a more rigorous outlook of being part of a bigger picture.
Several ideas include one game pre-Shepard called Mass Effect 0 or "First Contact War" and you could play as Anderson (or his Female XO for general sake) as you follow his story up to the point Shepard becomes his XO.
Another could be an MMO which puts you at the hub of galactic affairs post-Shepard as the game tallies the decisions of all players throughout the games to get the most canon result.
Or, as suggested before, gimmick games like Mass Effect Karting with Big Head Mode! I'm actually hoping mini-games will play a larger role in ME3 or at least Shepard's role in the Galaxy is not too stated to define if Mass Effect will be around or not.
Whatever happens ME1 and ME2 are large enough games to appreciate until ME3 so we'll cross this bridge when it arrives. I just hope they are loyal to the fans and don't hold back if ME3 is going to be the last because what do they have to lose by being controversial, epic, and innovative all in one?
Keelah se'lai!