I think Takahashi is the main cause which made the announcement this late. They (IMG and Kinoshita group) wanted Takanashi's participation but he was not ready for a "competition". I assume he doesn't want to give an impression that he's "finished" at this point. Inviting both Takahashi and Hanyu is not likely because Takahashi always wants to dominate the spotlight. If he knew that Hanyu was (also) invited, he would turn it down. In that case, they could've wanted Hanyu at least. But he was already taken by Finlandia trophy. The choice between Machida and Mura is not so important. Probably the JSF has given it to Mura because he has his own family (Machida is from a fairly rich family).