I'm planning on keeping mine even after I get my XBOX One. I'm a late convert to XBOX 360, I used to be a Playstation fan, and there are a lot of games on XBOX 360 I will no doubt still enjoy playing after I get an XBOX One.
Plus Microsoft plans to continue support for XBOX 360 for the nexr few years, so the console still has some life in it. So I've got plenty of time to enjoy my XBOX 360. I'll still be able to play HALO Reach and Combat Evolved Anniversary even after I get HALO 5.
I am still hopeful that backwards compatability will be worked out in some fashion, either as a peripheral or in the form of XBOX Live downloads.