I have all three and as far as the 360 goes I'm on my 6th or 7th and you know what? I'm still there day one. The features that MS has brought to the table, the marketplace and the robustness of Live along with Halo goes a long way. I have even bought into a second system with the Slim, and it seems far more reliable, so if they can match that quality there shouldn't be any issues next gen.
My Wii comes in second with all the first party Nintendo games and the VC, and PS3 a distant third. It's great, but all cross platform purchases go to the 360 due to Live and a superior controller. Their first party titles are good for rentals, just not worth building a third library for this gen. So mostly it has become the BD player. Honestly, if they stick with the Dual Shock again, I'm totally out next gen. That thing was an outdated turd when the PS3 launched, let alone whenever the PS4 comes along. It's a relic that needs to go away. That would be like launching the Wii2 with a slightly revised N64 controller. It's absurd they haven't evolved with the times.
My #1 want though is backwards compatibility across the board, that includes retail games, XBLA games, DLC which includes Rock Band tracks. Controller BC would be nice, but they would be shooting themselves in the foot if instruments weren't backwards compatible.