I agree that 20 can be annoying for a lot of guilds, as they end up either ceasing progression or disbanding due to the “roster boss”, but with the way raid buffs work right now, I dont think a 10-man raid is viable for mythic difficulty. There are 5 raid buffs, which we’ve already talked about here: External cooldowns/buffs on other players in group settings - #3 by Bababoey-draenor
Where we discuss that it would be nice to see these 5 buffs added to other classes so that having at least one Mage, Warrior, Priest, DH, and Monk is not 100% mandatory, but that love gets spread around.
This is a kicker for sure, especially for people who maybe want to reclear on alts. We spend a lot of time grinding out conduits, archivist rep, torghast, etc, etc to take an alt into mythic raid, all of which we’ve already done on our mains.