I find this a pretty surprising development. One would have to think if he's considering an endorsement at this point he has a reason. I agree that if he endorses it's either Fitzgerald or Thompson, and you would think the loyalties to both are near equal.
Does he support Tommy and think he needs it to win? Or does he think Fitzgerald is the least damaged going into the general election? Tommy needs help with the conservative base and an endorsement from Walker would clearly help. The only reason Fitzgerald isn't the "right of Tommy" pick is because conservatives don't thinkn he can win. A Walker endorsement might change that.
It would be puzzling to me for Walker to raise this possibility and then not do it. But if he's going to do it, he needs to do it soon.