As someone who has only followed this thread in a cursory manner, I am frankly a bit confused by this term "mother may I" - both what it means and why it is even used, or useful, at all. For me, D&D has always followed a similar pattern:
A PC can do anything they want to do, as subject to their statistics, the rules, and DM's discretion. If a PC wants to do something that is not clearly defined on their character sheet, they tell the DM what they want to do and the DM offers a ruling, based upon their best judgment.
How often this occurs really depends upon a lot of factors, but mostly the personality of the individual player and how much they like to play "outside the box" of clearly defined rules and stats. I've had players who never do anything that isn't clearly defined on their character sheet, and players who constantly come up with all kinds crazy ideas that are generally entertaining for everyone at the table.
"Mother may I" just seems to be a really weird characterization for that gap between clearly defined rules (and the character sheet) and the DM's adjudication - a term that doesn't really seem to need to exist, because it describes an element of the game that is, well, just an organic part of the game.
A PC can try to do whatever they want to, but it still comes down to a ruling at the DM's discretion. This is D&D 101, no? I understand that different groups hew more or less closely to the RAW and there's no one right way to do things. But I've never been in a group in which PCs couldn't improvise or do things that weren't clearly defined on the character sheet.
As a DM I've always encouraged improvisation. Actually, at one point during the 4E era, I found that due to the AEDI paradigm, players rarely improvised outside of what powers they had so I created a house rule that tried to encourage improvisation.
A lot of this comes down to trust and mutual respect: Trust in the DM's adjudication and, yes, ultimate authority; but also mutual respect - including the DM respecting the desires of players. Some people seem to take issue with that basic element of D&D, that the DM holds ultimate authority. I realize that some games take a co-DMing or more collaborative approach, but my point is that MMI is a completely useless term in a game in which the basic assumption is that the DM runs the world and where the buck ultimately stops. Meaning, unless you're playing a fully and equally collaborative approach, the buck still eventually stops with the DM and their best judgment.
That premise is baked into the very fabric of the game; again, there are variations, but they're just that: variations. The term MMI seems based upon a complaint about that basic approach, as if the players should be able to over-rule the DM's authority, or worse, implies that DMs are generally--or at least frequently--untrustworthy, and the players need to be protected from them by...rules? And if that is the case, I think there are much larger problems to deal with, because if nothing else, the social contract of a D&D game requires basic trust and mutual respect.
