Sounds like a cool idea! I’d play this.
Capture the flag (idea)

Interesting idea, but I feel like this is still too similar to KOTH. Maybe instead you would have to go to the opposite side of the board with your king and then make it back, making it more end-game based.

Possibly a normal board, but in between the king and queen on both sides is a white or black flag, depending on the side. You must capture your opponents flag and place it next to yours to win.
If you get their flag and place it at your side, but they have your flag, you do not win.
If you capture a enemy piece which has your flag, it is dropped, and to retrieve it, you must capture it (be on top of it, pawns can capture sideways or forward)

Interesting idea, but I feel like this is still too similar to KOTH. Maybe instead you would have to go to the opposite side of the board with your king and then make it back, making it more end-game based.
That's @HorribleTomato's idea.
Capture The Flag is already a Daily variant played on the CC forums.
I do not know if there is a place I put my ideas for a variant, so I put them here.
My idea- capture the flag.
Rules:
your goal is to bring your, king, to the center of four squares (like KOTH.), but the game doesn't end when you get there. You must bring the king back to its original back rank with the flag captured to win.
There is only one flag, once it is captured the other person cant get it.
If after 20 moves the flag has not been returned to the back rank, then the flag is put back in the center up, making it anybody's game again
the setup position is the same as normal chess, but the center four squares are always lit up by a color
checkmate rules apply, there is no capturing the king to take the flag away. You must stall the 25 moves
king is the only piece that can capture the flag
Setup
setup as a normal board, but all four center squares are light up until the flag has been captured.
so like this:
and it is light up until one of the kings has moved to that square, than the king will be holding a flag indicating that it has the flag. (not great at photo editing so I couldn't make a design)
thoughts?