A return of the NullStone?

[Cleretic]

Personally I think they should make the major side stories mandatory if and when they fit the MSQ. Unikalhai and Cylva should be a major players right now, but instead they're completely ignored because optional sidequests.

(Not that I think everyone should be forced to do the ShB role quests, but locking such story behind them was weird in the first place.)

I think the thing there is that for the most part, they approach with the mindset that every time you can plausibly link something from a side-story to the MSQ is a bonus for the people who played both, rather than mandatory to understand and appreciate either. You don't need to play the Alexander raids to understand when they come up in Shadowbringers, it just helps if you do. The only exception was the Crystal Tower, and that was because after a point the MSQ literally did not function as a story without those events having happened.

If I'm completely honest, though, I suspect G'raha wasn't the actual reason for that so much as the decoy reason; they actually needed to make sure everyone knew Xande and Amon for Endwalker, and the World of Darkness for 6.x, but also needed to keep our guard down about those things becoming relevant because they were all surprises. So pin the requirement on G'raha, give everyone a cute boy to focus on, and then wait over a year before revealing the real reason for the required reading. So I think in terms of going 'they should make this raid canon', the question shouldn't just be about the specific related events, but also how many plot hooks that brings over; the Crystal Tower had a lot, while Mhach actually has remarkably few.

You're right that Cylva and Unukalhai are in a funny space, where they feel like they'd fit just fine being made MSQ-canon but their barrier is too high to ever make that even remotely plausible. (I'd not just point out Cylva's requirements being 'every role to 80', but also Unukalhai's being 'very strongly imply you need to do Extremes'.) I'd also point out that C&U's story can only really bring over C&U themselves, since unlike with the Crystal Tower there's not really a great wealth of worldbuilding that only exists there, it's all expanding on stuff already in the MSQ. However, I think the developers very much know that, hence their dialog updating immediately, and I assume the stories will progress in parallel. Their goals don't exactly intersect or contradict (C&U's 'find a way to fix the Void' versus the Scions' 'get rid of that asshole making the Void a living hell'), so they can do okay while never needing C&U to cross over to meet Y'sh and Zero.