Pence isn't going to do it, but presumably they would have the 11 people needed plus Pence sign a piece of paper behind his back.
OK. They've got the piece of paper signed. Now what?
And once the 25th Amendment has been formally signed, sealed and delivered, how do people learn that it's happened?
The whole procedure is fraught with risk.
It's not so much that anything dreadful is bound to happen, but there are so many points at which things could very easily go wrong, and with potentially catastrophic consequences, that Pence, if he's thinking on those lines at all, must be thinking very hard indeed about how to proceed.
To my mind, Pence's duty is pretty clear -- Trump's obviously incapable -- but so is his duty not to make a dreadful situation even worse.
Quite apart from his actual motivations, I'm really not sure what the least bad course of action would be at this stage.
I don't think the 25th Amendment was designed for this -- it's for when the President is incapacitated in the sense of flat on his back in hospital and unconscious, not when he's ... well, whatever the word is for Trump's condition at the moment.
"Manic"? "Delirious"? (Obviously there are plenty of words I could use, but I'm trying to think of something neutral you'd put in a legal document).