[jerf]

As others have mentioned, that is accounted for in the rules.

My immediate first reaction was also that it would be interesting to have a variant that is the same except you are allowed to checkmate, except then I realized the recursive nature of how board positions are evaluated makes that problematic. For instance, if there's a mate in 2, the first move of the mate in two is now certainly the "best move". Creeping up on a checkmate without ever making the "best move" until the very last one might actually be harder than the win condition based on strangling the opponent described in the current rules.

[sovnade]

It just doesn't make sense though for that reason. You can't sneak up on an engine. There's not a single engine out there that wouldn't recognize a mate in 2 moves. Unless the opponent blunders (which actually might be forced if the best defensive move is blocked).

It just seems like you're changing the objective of the game entirely to the point where it's only slightly related to chess.