I would have to say that ASP-C, ASP-H and FF sensors will still be around for a long time. Why? Consumers have become accustomed to the formats found in current DSLR's and manufacturers won't just "up and change" formats without a long period of gradual changes to get people used to the new "formats", if and when they ever become available. Heck, the current digital sensors were based on now "obsolete" film formats to help film users make an easier switch to digital! Why APS-C? Why 35mm? Why not some other random sensor size instead? Why didn't Canon just create whatever size sensor they wanted? It's because of the thousands upon thousands of film users out there that they had to convince that DSLR's were the way of the future. What better way to do that then offering a product that was compatible with their current lenses and conformed to known film sizes for crop factors!
Don't believe me? Look at the gradual changes in automobile designs even though everyone has known for decades that certain aerodynamic designs work better than others.
Personally, I like having the option of the 1.6X magnification when I need it without having to buy more lenses or teleconverters!
There are advantages and disadvantages of all the camera bodies, one simply needs to choose which body is best for their needs AND budget. There will NEVER be just ONE camera body produced! Unless of course they find a way to tap into your optic nerve and brain and you could process whatever image you want, however you want, just by looking at it and thinking you would love to have a photo of it!
I have the advantage of having crop sensor bodies and FF bodies to choose from, so I just pick which one I want to shoot with that day.
Honestly? As much as I love my new 5D2, I wouldn't give up my 7D for anything. And for the cost, you can keep the 5D3!!! (my opinion)