Honestly, if there is one area I think Blizzard has really dropped the ball with BFA, it was the idea of not doing Class Sets anymore. Without Class Armor to go after, I legitimately don’t see people ever really doing transmog runs for BFA content (the art team made very BELIEVABLE armor, but very little felt truly COOL, imo).
It looks like that policy is continuing in Shadowlands, and honestly it’s a big ol’ bummer. I really miss having all those cool Sets to go after, they were a significant reason I kept playing the game. With their removal, it made it easier to ever to quit in BFA.
Personally? I would love to see another set of Challenge Mode sets to go after. Hell, I wouldn’t even mind bringing back the MOP CM sets, provided they are just as (or even more) difficult to complete. I got all the ones I cared about already, but the content was fun and the sets were hella cool (certainly more than the inferior reskins used for Legion class hall sets).
My rationale for CM armor again is that you can truly base it around THE CLASS, and not THE RAID. I think Firelands, as much as I enjoyed it as a raid, had some of the worst sets in the game, for precisely that reason.
Just my two cents. If nothing else, perhaps have a Set for each Class for completing content across the whole expansion?