I mean... look at how many adults in this thread are gutted over a 1946 movie & 1989 ride... if it still means so much to them, I'm sure PATF will for years to come. Especially for young girls who see tiana as the only princess who looks like them.
I think a lot of people just don't have as much faith in current management as you apparently do when it comes to destroying an existing classic attraction to turn it into something else.
A re-theme by it's very nature means that there will be considerable creative compromise made as they attempt to fit the new theme into the existing space. Think about how we got a low capacity boat ride for Frozen in the wrong park that has visible pipes in the way of one of the opening scenes as you go up the initial lift hill...
Also, look at the description of the ride - taking place after the movie while they get ready for a Mardi Gras party. That means, to continue with the Frozen theme/example, we can look forward to a
Frozen Fever type of story taking over the existing story that actually has serious and some might argue slightly frightening themes that feel appropriate for what is essentially a thrill ride.
I'm happy that Princess and the Frog is getting an attraction. I thought it was a great movie that didn't get the attention it deserved simply because it wasn't computer animated.
I'm happy that due to the bones of what they are starting with, it will almost have to be better than what we got with other recent princess rides like Little Mermaid and Frozen but I'm sad that it will probably end up being less than what it's replacing.
If current Disney wasn't already known for corner-cutting and if the company as a whole had a better track record when it came to doing rethemes of existing stuff, I'd be a lot more optimistic but I fully expect the replacement to not meet the standards of what it is replacing, much less exceed them.
If they do, I'll be shocked and thrilled but mostly shocked.