what then? It's killing me! What?!
Impossible to know, but:
A. The Draconic Subclasses and Fey Lineages seem to be for the same product, based on UA timelines.
B. The only products to have both Subclass and Lineage options are Setting books.
So
C. These appear to be for a Setting book.
Of course, they could be for separate books, or they might put Subclasses into a Monster or Adventure book for the first time, or something more radically new.
If we grant that these products are for a Setting book, there seem to be four main possibilities:
1. A Classic D&D Setting. This seems improbable, as both UA tests do not fit any existing Setting in particular, but it could still be what's up here.
2. A brand new in-house D&D Setting. This seems least likely, for sundry reasons, but it's possible.
3. A licensed Setting, similar to Acquisitions Incorporated, Rick & Morty, Wildemount, or Stranger Things. This is the real wild card here, and quite plausible. I have no idea what this might be, but it would not shock me.
4. A Magic Setting book. The four big Sets for Magic this year are Kaldeim (Norse myth stuff, would be great for D&D, but these options don't seem to fit), the Forgotten Realms (I could see some sort of tie-in book to the upcoming card Set, not sure these options scream "Forgotten Realms" though, and SCAG already exists), Innistrad (Gothic Horror, doesn't fit any of these options in the slightest, and I wouldn't be surprised if it gets name checked in the Ravenloft book, and mist interesting in my mind (obviously), Strixhaven. Strixhaven is a brand new Setting, about which the Magic team hasn't really started getting deep into yet. The cards come out at the end of April (a good time to announce the next book after Ravenloft, potentially). It's a magical academy Setting, with Elder Dragons playing a foundational role, and owl people (among other Fey shenanigans). Because it's a new Setting, I really wouldn't expect WotC to put out a D&D book for it...but stranger things have happened.