I think he's free to do what he wants. He doesn't owe anybody anything. It's an open market, too, so if anyone cares to step in and make the next best thing nobody is stopping them.

I'd go as far to say that he has every right to charge for TM2 when it comes out, even if he promised it would be a free upgrade.

EDIT: even though I've stopped using it, I use vim now :)