99% of the time it wouldn’t matter whatsoever because NA gets early access to extremely broken or overtuned bosses (with Soulrender proving this heavily since the pre-hotfix version was easily the second-hardest boss in this raid if you could count the last three before Sylvanas being cheesed), but if Sylvanas ends up lasting the rest of this reset Limit will have a MASSIVE advantage, assuming they will jump straight to splits and will reclear Mythic to get even more gear.
That said, it’s a tricky situation. Sylvanas is theoretically possible right now, but she’s not going to drop without a fight. The guilds need more Rogues, and any Boomkins not playing Venthyr right now are trolling if that’s what it takes. And if she lasts another reset and the guilds decide to reclear, they may very well end up having to rekill a much much much harder Mythic Kel’thuzad, since there’s a 99% chance Blizzard is fixing that trinket cheese.