Since this, in itself, is not a spoiler anymore I have removed the tags.
Bioware have stated that the Mass Effect franchise will live on. And they have hinted on that whatever comes next takes place after the ending, sans Shepard. Personally I am quite excited, actually. The possibilities are endless, almost. Maybe they in the end will treat the first three games as the equivalent of the fight against Morgoth; an incredible detailed backstory a long time ago.