I think it is very important when considering a system like this to decide EXACTLY what problem you are trying to solve. A lot of the comments focus on making it "easier" to identify or close game-rec questions. I don't think that is a problem we have. It is very easy to identify game-rec questions, and they get closed very quickly.
If the problem you want to solve is eliminating the hard feelings when a new user posts a game-rec question and it gets closed immediately, then you would have to solve it before the question actually gets posted, as in the original suggestion. If done well, this does seem like something that could help solve a real problem. However, I'm not sure if it can be done well.
Is it even possible to have site specific question recognition (similar to what we already have for subjective questions)?
If it is possible, can we make specific enough to avoid lots of annoying false positives? You can't just look for the word "recommend". You'd need to look for phrases like "game similar to", "games that are like", "What games are like", etc.