Broadly I’d say these are bad ideas.
Everyone should agree that more people playing the game is better. The game having a lot of players is more important than this problem of “a scrub wants to join my M+ group.” For one thing, Blizz makes more money when there are more people playing, so we know where they fall. But for another, you can screen your applicants and choose whether you want to group with them or not, so “there are scrubs in the group finder” is not really a huge problem.
What’s a problem is this - there were 2.4 million Mythic+ runs in the first week of this season. Last week, there were only 716K.
Engagement with M+ has dropped by 70%.
This undoubtedly translates over to more unsubs and fewer players and the emptier group finder that we can all observe in game.
This is a long-standing issue for many seasons.
So how do you fix this, well ideally you make the content more fun for more people, which a difficulty boost and a mandatory grind of lower keys like the OP wants probably isn’t going to do.
But barring deeper mechanical changes, you just give them more rewards. People basically play for a combination of fun experiences plus character power gains, those are the reasons they stick around.
So if anything, Blizzard should progressively nerf this content over the course of the season - probably not through random haphazard surprise mechanic changes, but through an actual system. Handing out more and better gear is the most fundamental system for this! But borrowed power systems work too (despite all the hate for that term). E.g. damage and HP increases tied to participation.
Because as it stands, all we get are people posting that the harder jobs like tanking are not fun, and then they quit playing.
There are numbers out there on how many M10+ completions are happening every week. Despite these players being very vocal, they are a vanishingly small percentage of the player base, and it’s shrinking.
I don’t get why Blizzard is so stingy with rewards when it causes engagement to drop 70%+ over the course of a season.