Heroes of Might & Magic III: Horn of the Abyss

It would be interesting to see the implementation of unused animations for old creatures (Hex-Attack).

Exactly, this has been discussed for a long time – even before the team was organized and the idea for the add-on was conceived, there were plans to release a mod using everything that the developers "forgot" in the unit animations.

Will old bugs from the time of SoD be fixed?

They will be.