I mean, I would expect the 6600XT to have 8GB at least as the 5500XT has 8GB and 4GB models, like the Polaris-derived siblings did before them.
The fact they'd make a 6600X (or without moniquer) with 6GB will come down to whether or not they want to keep the full BUS width, but at this point in time, it would be sincerely weird for AMD to do so. Going on a big assumption, the dies used for them would be lower binned parts of the full 6700XT die, so I'd imagine it will come down to the "harvest". Strange, but not impossible, I guess...
In any case, anything above 4GB in this day and age is welcome; nVidia should* take note... Seriously.
At this point in time what does it even matter what they come up with, ALL gpu's are ridiculously way over priced, sold out, scalper prices etc.. waste of time, why even bother even planning on a new pc build right now, only the lucky can get a gpu at msrp IF your near a Micro Center, or the wealthy that $2500 is a drop in the bucket and those prices don't faze them, and of coarse the youtuber's that get gpu's sent to them free for reviews, I'll just wait for all this BS to blow over, I'll stick with my Intel 6600k & R9 390 works just fine.