I can understand needing to alter some things for 3D, like ensuring proper non-nauseating focus, or maybe there's missing geometry out of shot which the slightly repositioned cameras would expose. But this bit doesn't make a lot of sense to me:
Furthermore, the original movie was made for cinemas and was 24fps; a lot of changes to the animations had to be made to get the correct results.
In any game engine it would be trivial to adjust 1/48th exposure and 24fps to 1/120th exposure and 60fps. I find it difficult to believe animations would be keyframed to 24fps in a way that couldn't be correctly lerped.
Can someone explain in more detail the challenges they faced?