It's not general AI, no one said it was. It's similarly not going to play checkers at the drop of a hat like KJ could.

The thought experiment a little more refined, like alphago programmers get time to implement only validMoves() and makeMove() then let the same learning process go on it, I wouldn't count it out. If you only flip the switch once the new game variant starts, before a human has even begun to take an action the computer will have played out thousands if not millions of games using MCTS and slowly training up its networks in real time instead of using a static one. As the game progresses the bot should only get better and better.