Hey, have you had any progress prototyping maybe? I had similar idea few months ago and left this google page hanging for a while, it refreshed and gave me your post in top.
Chess Variant Idea (pieces with a health bar)

Yeah, I've been thinking about that. I have a few different ideas: 1: the king must be checkmated (so check rules apply), 2: the king must also be "killed" but has a ton of health, 3: the king must be killed but other pieces of the same color can be sacrificed to increase the health of the king (but only when the kings health is negative). Many things can with done to the king, not sure what to choose


That was already my idea. In your former example the bishop would do 3 damage and "die", meaning it is no longer on the board.
Recently I had a very interesting idea for a chess variant. Each piece on the board has a healthbar, which initially has as much health as how many points the piece is worth. The pawns have 1 health each, the queen has 9 health, etc. When piece A captures piece B, the health of piece B is subtracted from piece A. For example, if a queen with 9 health captures a bishop with 3 health, then the queen has 6 health afterwards. If on the next turn a night with 3 health tries capturing the queen with 6 health, then the queen WILL NOT be captured, but the night will "die", and the queen will have 3 health remaining. Another idea I had is that queens, bishops, and rooks have a special ability, that they can take multiple pieces at once. For example, in normal chess, after a piece captures another piece, it "stops". But in this variant, a piece can keep moving and capture more than one piece in one turn, but only if that piece has enough health. If this mechanic doesn't make sense, ask me and I'll try to describe it more clearly. Another idea I had is that pieces can move to their home rank (1 for white, 8 for black) to regenerate one health each move. They cannot regenerate more health then their original health. This variant is still hypothetical, since I hadn't made any playable version. I'm eager for any questions and comments.