You should probably write this explicitly on Steam and in this itch.io page. Maybe consider giving it a name to qualify the more complete version on Steam?
Bonus questions:
- Do you intend to upgrade the Steam version or is it definitive?
- Have you saw other examples that pre-date yours (as you said a lot of clones have been made after your game)?
Ideas:
- There could be a time/blitz mode? (this definitely could be speed run!)
- Level editor (as others have said) and a way for user to share (I don't know how much interests + actions there will be, but that is sure an interest idea to potentially have more content)
- More levels (as others have said)
- Etc. (I have not give it deep thoughts how this game can be improved, but since it can be beat relatively quickly some would want more after paying even if it is not priced that high)
All this being said, I really enjoyed beating this version, level 24 was an interesting challenge. Very clever usage of chess to make a puzzle game. THANKS! :)