They absolutely can back out. There is nothing dictating they must move forward with this at all. The whole thing was a knee-jerk reaction to begin with. If they announced they were building a PatF-based ride at DHS and this was cancelled, no one would bat an eyelash. If this was cancelled/never brought up again, who would care? Those who are told to be outraged?Realistically I think D23 is a possibility for more information but I still doubt it. Disney announced this project too early, and they can't back out of it. The publicity would be outrageous backing out on a change like this.
So now Disney is forced to spend the money to redo Splash Mountain. Quite possibly they may even offer to pay for Tokyo's in the future too. For now there's just so little information about this project that who knows what will happen.
Arguably Tokyo would be the hardest to change because not only do you have a ride, you would have to redo the quick service place attached to Splash Mountain for it to fit thematically.
And Tokyo isn't changing theirs.