I also think so, with "Guildmasters guide to Ravnika" they stated the guidelines of "Dhampir-like" races and guilds, so I assume if they create a half-vampire race It would be tied to the races and guilds of that setting. If they revive the Vrylockas those could be perceived as too similar to the ones in Ravnika (Yeah, I know they are not, but they are in a surface level)
Ravnica has more regular Undead Vampires and Mind Vampires, not the playable living Vampires like the Vryloka are more Zendikar, Innistrad, Ixalan, and maybe a few others. Although Vryloka is the Greek type of Vampires, so they in particular would fit on Theros.
