I think it is already there
Expansion of Move Confirmation Button
Sorry I should I have specified that I was referring to the desktop version. Yes you're right, the confirm move option is already present for mobile, but not for desktop.
Thanks @ryry, I had forgotten that's an option for getting confirm move for all live game time controls functional on desktop. Still I think it would be even better for the sake of consistency to also add it to the desktop browser settings so that more people will discover it and decide which they prefer.
For daily games, I have the "Confirm Move" option selected on. I would love to see this option expanded to include rapid games as well. In the 15/10 rapid game I just played today, I was trying to castle but screwed up and clicked just a hair too far on the wrong side of the dividing line between squares, resulting in just a one-square step for my king rather than the necessary two-square step to castle, thus boxing my rook into the corner. This and similar mis-clicks have happened from time to time in live games where a confirmation box could easily have saved an entire game. I've also occasionally seen it in opponent's play where it looks quite likely to me that they didn't mean to click the square they did, the logical choice typically being one square adjacent. Of course it would add a few seconds or to each move, which would be the user's price to pay for the confirmation and mis-click prevention, which means it would probably not be practical for bullet games, but I think most people would find it to be beneficial to eliminate this source of frustration for 10 minute to 60 minute rapid time control games, similar to the reasoning it is included already for daily games.