Prophecy2k
Veteran
Backwards and platform compatibility might be a bigger thing this time. It would mean you can still hook up with friends on the old console.
In addition to that some of my hardcore friends on Live are in love with their gamerscore.
Regardless of whether the next-gen consoles are backwards compatible or not I expect trophies and gamerscores to carry on into next-gen.
However of course you won't be able to take your gamerscore over to PSN if you decide to switch platforms next-gen. At the same time though I don't see anyone remaining with a platform and platform holder on the sole basis of a gamer score. There are far more important things that will hold a greater sway on people's decisions whether to switch or remain next-gen. Plus, your xbox gamerscore will still be alive on PC with GFWL (or whatever MS call their Win8 version), and given the rumoured specs of these next-gen boxes i can see many investing in a high end PC as well as their consoles, in order to satisfy their rabid and insatiable grafix whore desires.
I personally see many being happy to switch consoles if given enough reason to. I certainly am, and that's considering I've never owned an xbox this gen and have never really seen any reason to.