Add this post to the long list of reasons why we are platonic soulmates. I have uesd my left hand almost exclusively since I discovered its awesomeness. The right is too “perfect” so there isn’t enough stimulation.
As for the quesetion, it will almost certainly be as people have said… most will move on although SF4 will still be around. If they do it right, there shouldn’t be much of a reason to play SF4 anymore. SSF4 should have all of the good things that SF4 has combined with better balance and new stuff that makes it even better. Should is the key word, of course. If the game is somehow really broken or Capcom manages to FUBAR it somehow (which I doubt but you never know), SF4 might remain the standard.
Whether the game is released in the arcade will also impact its future. If it is console only, I’m sure that some purists will prefer SF4, especially people in places like LA and NYC where there are some who don’t even own the console version.