If they ever did a live action Hunchback of Notre Dame then Charles Dance should be cast as Frollo. Unfortunately the movie has too many "dark themes" to be considered "family friendly" and is considered one of Disney's darker animated films. A live action Hellfire song scene would've been awesome.
A live action Disney The Black Cauldron film will never see the light of day even though they could market it as a Halloween horror flick that could appeal to older fans. However they would lose out on the family market which is considered Disney's bread and butter. The Cauldron born scene was creepy enough animated, in live action it would be even worse. However the special effects for such a film would take up a large chunk of the film's budget and sometimes what looks good in animation doesn't look as good in live action. Also if they did try to market it as a Halloween movie, it woulld be going up against Hocus Pocus which is considered a cult hole and is also more family family so that will win out every time.
Atlantis would've probably been a good underrated film to be reproduced in live action. it's not one of the "big" iconic animated films like Aladdin, Beauty and the Beast, Lion King, Frozen etc but it has a solid story and a diverse cast of characters which would certainly tick boxes for Disney.
Treasure planet (which is basicallyTreasure Island in space) has the issue of basically being a pirate movie when pirate movies aren't popular outside of Pirates of the Caribbean. The pirate genre was considered dead in the water until PotC came along. Also the muppets already did their version of Treasure Island. Given that the muppets did one of the best versions of A Christmas Carol, I think there could be an unfair comparison between the treasure planet movie and the Muppets treasure Island.
I also think one of the problems Disney has with some of the remakes is that the TV show Once Upon A Time did it so much better. Snow White is a clear exampe of this. OUAT Snow White still had the iconic beats of the Disney tale eg Poison Apple, Glass coffin, True Loves Kis, 7 Dwarves etc but it sill had a more proactive Snow White (at least in the early seasons) and wasn't just "girl waits for prince to rescue her".