Allow nonce customization and other power user options, or at least not block it - I went to my ether wallet to sign replacement transaction manually - as I wanted to do another transaction instead of pure “cancel”, everything went smoothly but MEW didn’t spit out signed transaction, instead metamask sent it automatically to network, so I couldn’t review the transaction blob before getting it sent, thats one, second is that MM automatically supplied nonce, instead of allowing me to replace pending and stuck transaction (by accepting nonce I supplied to MEW). So I had to cancel previous one using metamask anyway, and waste some ether for 100% unessesery gas fees.
Allowing more controll for people who know what they are doing would be awesome. Same problem is with MEW, to be frank, and MM is doing admirably good job of finding the middlegrounds, still I think there are places for improvement - like this.
And yes, I am aware of advanced settings, and I admit I forgot in the moment about their existance, as I have them disabled on my personal machine (enabled on my dev machine).
My point is that if external dapp asks for nonce X, it would be nice to respect that or show big red banner “nonce looks wrong” with some link to explainer.