The World Cup should keep many skiers away as getting a hotel won't be easy. Unfortunately, it doesn't look like they're guaranteed to be top to bottom for Thanksgiving. If there was no World Cup, that would mean 30+ minutes lift lines in the North Ridge.
When Killington has only the North Ridge open, they are seriously limited by lift and trail capacity. The triple can only handle 1,800 skiers and hour, but stops a lot when crowded, so it's probably able to actually do much less than that. The acreage is not enough for the crowds they get come mid November. If they're not t2b by the week before Thanksgiving, there will be tons of skiers on the trails, with the rest piling up in the lift line below. I applaud Killington for always being open early for anyone who wants to get out then, but I wouldn't go this late unless it's top to bottom.
When they do get top to bottom, the K1 becomes a skiable lift (instead of running only for access) and they add the Snowdon Triple. The North Ridge Triple remains open. That more than triples the available lift capacity, so the lines are almost nonexistent at that point. Trail acreage increases by a similar factor, giving much more room to breathe.
If they get top to bottom, I'd go for it. Just expect to be parking far away and taking the shuttle bus as all of the KBL parking lot will be full because of the WC. As of now, they don't appear to be blowing a second trail on the Superstar area, so that lift definitely won't be open during the event. If it was a cold November, they'd open the Ramshead and Snowshed areas for Thanksgiving, which would mean you could probably park without having to take a shuttle to get to a lift. That just doesn't seem likely this year.
I've lived in New York my entire life.