To be fair, they did describe the Anniversary collection as the first Anniversary Collection, so at the very least, they do plan on doing at least one more collection.
I don't see them including any of the 3Dvanias in the package, nor do I see them using any of the DSvanias, since they'd actually need to be changed quite a bit to work on anything that isn't the DS or 3DS.
Ideally, what I'd want out of a second collection, assuming they're doing 8 games again, is:
-Adventure ReBirth, which is impossible to purchase now.
-Castlevania Chronicles, especially since it's technically two games
-Castlevania Legends, which is especially hard to come by these days
-Circle of the Moon
-Harmony of Dissonance
-Aria of Sorrow
-Vampire Killer
-Haunted Castle
And then, additionally, it'd be nice if they made Requiem multi-platform instead of a PS4-exclusive. Maybe do an update to put DXC and Dracula X into the collection, same way they updated the first collection to add the Japanese versions of the games?
If they did do the 3D games, though, it'd be nice if that were its own separate collection. Just CV64, LoD, LoI, and CoD all in one package. Or if they wanted to be lazy with it, just cut CV64 (though I prefer the stories of the CV64 cast in the original game rather than their LoD versions).