what you think Sprint will do? Just say eh, and move up or will be another updated to fix the battery issue.
My guess is with all the new devices coming this year the EVO will not receive anything beyond 2.2. Maybe some tweaks here and there. Concentration will be on newer, dual-core devices that can run apps like the tablets can.
On the flip side of that.....the new Kyocera Echo has about the same specs as the EVO so if it gets updated no reason why the EVO wouldn't. But, who knows. Personally, I don't see the Echo having a very long shelf life.