Hi!
While we will certainly keep supporting Mesen within the same conditions that were previously outlined, I would like to direct players to the following:
https://github.com/threecreepio/mesenrta/releases
This is a Mesen release compiled by threecreepio for the SMB1 community. It basically strips the run-ahead feature and shows the input display by default on screen. I would definitely recommend speedrunners using Mesen to move to this fork of Mesen as I'm sure more and more games will follow in SMB1's initiative and allow this fork.
Enjoy!