Agreed...and I do not know.I think it also depends on how much time Harrison Ford is willing to commit to the franchise. If he is signed up for just one movie, this is definitely a possibility.
I do know at an interview/press conference with him, Mark Hamill, and Carrier Fischer, that the latter two seemed much more excited and viewed the new movie as sort of a re-birth.
But it appeared to me that Harrison Ford viewed it as pretty much just another movie with him in a leading role. He did say that at the end of the last three (Star Wars I-III) that he never expected to do another one, that he thought it was over.
So, from that you might extrapolate that he does not see himself involved in all three.
It will be interesting to see.