Couple of suggestions

[Nilex]

1. Undo button for occasional miss-clicks, and more common "dohh" moments. Can undo all moves from the start. Played a flash game recently with that mechanic and it did wonders for playing comfort without impeding gameplay or difficulty.

2. Visible number of rotations allowed to achieve "Perfect", or Trophy. So planing ahead has a bigger purpose and to reduce the number of trial & error retries of a level. Would work nicely in tandem with the Undo button.

That's pretty much it. Not too big hopefully but with a nice positive impact on playing comfort.
Nice job with the puzzle mechanic. Personal favorite is IV -> 14 which took me half an hour :)

[Darel Celsus]

same

[Dan_The_Noob]

would defeat the point of the game if you could just undo moves.

[Nilex]

It would is save time and frustration. QoL as in other decent software out there.
Anyway if it hadn't been implemented so far is safe to assume it never will be.