Pulling out some pieces from the slyflourish article. The tone of his article and his video on the subject suggests that the proposed changes are minor, but looking at the specifics I'm not sure this is the case
I want Monsters of the Multiverse to work with the new version of D&D. I want Tasha's Cauldron of Everything to work with it. I want Journeys Through the Radiant Citadel to work with it.
Characters from Tasha's work with PHB characters, yet many have noted that the former are more powerful, have more options, and more complexity. As I mentioned in another thread, the complexity was enough to turn me away from playing a Tasha Bard. Similarly, the types of options they put in the latest UA add a lot of per rest abilities. All of which is to say that compatibility is subjective, and could be broadly interpreted. Speaking of...
Better, faster, easier, and looser encounter building guidelines could help DMs quickly measure encounters built either before or during the game. Building a reasonably balanced encounter should be easy and fun.
High CR monsters are often weak for their challenge rating when compared to lower CR monsters. They often don't do enough damage to threaten high level characters.
Is this an easy fix? Shea recently said in a video that there was enough variability in 5e encounters that it would be impossible to precisely balance encounters. He has his own version of simple encounter building rules, but he acknowledges that he often wings it and the main toggle for him is between deadly and non-deadly encounters. Which works for me, but is different from the demands I see for very precise and reliable math for building easy/medium/hard/deadly encounters. Similarly, adding damage to high CR monsters is easy, but it seems that high level play brings a host of other problems. Will those be fixed?
Provide Less Problematic Race Descriptions
It wouldn't surprise me if one of the main reasons for a refresh of 5th edition is to cover problematic race descriptions like the racial essentialism of goblins and orcs in the Monster Manual. Other fans offer much better advice on this than I and I support such changes for a wider, richer, more interesting, and more inclusive game.
Very necessary, and I'm happy with the steps they are starting to take, but this is going to require a fairly extensive rewrite of some sections of the monster manual, including changing art styles for several entries (hobgoblins for example).
I don't think they are going to change anything too drastically. But, they could, and in some areas if they don't, I don't know they will meet Shea's criteria except in a very superficial way.