Well I wonder how feasible it would be deprecate some of the older features? And when I say "deprecate", I mean not just a warning, but completely removing it from the language.
I mean, it isn't as if your current projects automatically starts using the latest .Net version without your control. You usually have to tweak a project anyway when you switch .Net versions, so I don't think it is such a bad thing.
This will ensure that the language doesn't get too bloated just for the sake of backwards compatibility when there are new/better ways to do the same thing.