I miss the early days of Firefox extensions (circa 2004) where an extension could in very powerful ways completely change the layout/functionality of your browser; when they had near unlimited access to the XUL and could change anything and everything. I used a ton of very useful extensions then. Nested tabs were one of my favorites. These days I've got a password manager, a bookmark checker, and a tab manager I wrot…
Extensions systems which don't have very clear cut boundaries like XUL are just add a very hefty maintenance burden and make review extremely hard.
It's not really about "normies".
This doesn't really apply to the current change, as extensions already have clear boundaries and and as the article pointed out problematic apps likely won't be too much affected as they often already do things which bypass the constraints to avoid detection by the reviewer... (assuming I understand the topic correctly)