I'm trying not to come off as argumentative, but I don't understand your points.
If adding a book like a Greyhawk Adventurer's Guide would be disruptive to AL and the video game .... then as you said, those entities should ignore the Greyhawk release. If those November releases are so important, how did the AL and Neverwinter function with just ToD, PotA, and the first half of OotA before those November supplements??
Not following. The AL initially ran under three banners, one based around playing the latest AP, one based around the Moonseas, and one for convention play. What happened was the first two weren't crossing over well; all the fun was happening in in the SC and the AL was wandering around the Moonsea. So they merged the two and started making the AL adventures more relevant to the APs starting with SKT. Now, Yawning Portal was a bit of odd duck (you mostly just played the YP adventures + a few side quests for thee of them) but they are back (and even stronger) to tying AL play to the APs (including PCs getting the Death Curse).
If there was a Greyhawk (or insert setting here that isn't accessible to the Realms) they'd either completely ignore it (and do their own thing ala the Moonsea days), they'd have to suspend the Realms-based AL and everyone roll up new PCs for a season, or they'd take it port to the Realms anyway (thus ruining the point of the other world's uniqueness).
Remember, AL isn't just RPGA/tournament play, its the primary focus for supplemental material. The Pax West/Fathom event module was AL legal. In Volo's Wake was an AL module to tie in with the new book, all the DM Adept modules are AL Legal. WotC is working a lot closer with the AL as an outreach and recruitment tool.
If Curse of Strahd was a headache for AL, then I think it will be safe to say that a Planescape adventure would cause the same problems and it shouldn't be done.
The problem with RL was you couldn't leave easily (and thus, you could only do RL adventures while "stuck" in Barovia). A Planescape/Sigil adventure could, more easily, allow PCs to come and go via Portals.
The bigger question, do you want that kind of "come and go" of Faerunian adventurers wandering around Greyhawk? Dragonlance? Dark Sun?
My comment about my gripe has kind of derailed this so I'll finish with this. I stand by what I said, they should do a 1 and done book. If the November releases are so important, then how about allowing Goodman Games to do the Greyhawk book? They are converting modules B1 and B2 to 5E to be released Sept. 30th. This way, there isn't a disruption to the main release schedule and those of us hungry for Greyhawk get the bone we've been begging for. Plus, there is a Greyhawk book for 5E and WoTC has little to no risk involved for that release.
I'm cool with that! WotC outsourced some of the risk in 3e by giving RL to Arthaus and DL to Wiess's publishing company. GG could easily do GH. Or Kenzer (are they still around?) or Kobold Press, Sasquatch, Necromancer, Green Ronin, etc. The question is there enough will and finance to get those projects going?
Back on topic ....
I've read more Tomb of Annihilation and it just keeps getting better and better!
I have to wait until my DM buys it to run it, and we just started the StarFinder AP.
EDIT: to not derrail the thread further, I'll leave it at this. We'll agree to disagree.