As much as the setting would help you, I would have to *respectfully* disagree. It would help with people stalling games, although it helps a little too much.
Lets say you only have a lone king, while your opponent has a queen or two. As well as you both only have seconds remaining. At that point, personally I would be trying to win by time. & if you are not paying attention, and you only have one possible move you would lose. With the "trigger move" setting, you would automatically move, possibly winning the entire game.
As much as I would love to see this setting, I feel like it could be too much of a help, & cause unfair wins b/c someone isn't paying attention.
Should there be a setting similar to premoves, where if you have only one legal move in the position, the site would automatically play it for you in a tenth of a second just like a premove? It would need to be enabled just like premoves, but seems relatively easy to program. Sure the opponent may end up spending more time if he's winning trying to checkmate you while you only have a lone king, but usually you have at least 2 legal moves and since the opponent can also premove it seems fair. What do you think?