Suggestions made in chat should somehow be turned into real feature-requests to get into the usual voting process.
If I think about it, isn't the individual right there in real time? I won't get to test the chat until later today, but I'm guessing that the ideal scenario is that the user is right there and you can suggest to that user, straight in chat, to post it as a feature request.
Flagging implies either automatic action or moderator action is required. The former is not very wise - a feature request should be structured and tagged when posted to Meta, and this requires a human element. There's too much error that can result from trying to parse a chat to get the exact desired request as well as properly tag it. The latter is almost fine, except that the person who actually proposed the idea should get a say in making their own feature request. As well, we shouldn't make it the responsibility of moderators to make the feature requests that other users have brought up.