Well, there aren't any of the classic D&D fey hidden in Wild Beyond the Withlight or the Domains of Dread pdf.
Here's what I see going forward.
1) We've just been given a Fey-themed adventure so there won't be another one of those in 5e's forseeable future.
2) We've also been given the Domains of Dread mini-expansion on the Feywild, Fey, and Domains of Dread. On page 20 they even give a list of Feywild appropriate creatures by CR from the MM and Wild Beyond the Witchlight. This strongly suggests that there isn't going to be a ______'s Guide to the Feywild book coming.
3) We have the 4th monster book (Fizban's Treasury of Dragons) coming up next month, and it's about dragons, not fey. Those only come out every 2 to 3 years. I find it unlikely that they are going to give us a fey encore in a couple years and make them one of the features for one of those books--or even bother putting many as random creatures in the bestiary section.
With all that, I find the most likely scenario is that WotC is now satisfied with their fey offerings. Yes, we will continue to get statblocks of the Fey creature type now and again in other books, but they don't seem to feel like there is any need for brownies, spriggans, gremlins, nymphs, etc.
I think we can sadly assume that they don't consider "covering the bases" of classic D&D fey to be a goal.
Thanks for all the suggestions (and
@Quickleaf and
@the Jester and
@Sacrosanct, thanks for the conversions! I might ask for a couple more if that's alright). As far as the 3PPO, most of them just aren't doing what I want. I'm very strongly a "D&D in my D&D" player. I'm mostly concerned with conversions of classic D&D fey that maintain their feel. D&D just isn't my choice of games for more authentic folklore (I use different games when I want a more authentic feel). It also seems like the majority of PPO focus a lot more on creating entries for the fey that
they would like to see represented in the D&D game, rather than converting the fey that the D&D game has previously given us, so they include enormous numbers of probably really fey, but just a smattering of the D&D classics. I guess I'm just an old 2e grognard that would really like the D&D lore I love to be updated to 5e mechanics, but I doesn't seem like WotC has my back anymore.