Going by the story DLCs for Fallout 4 and Skyrim, I’d expect it to be mostly orthogonal to the main quest so that players can experience it regardless of how far along they are.

The DLC could require getting to some point in the “first act” (e.g: meeting constellation, or finding the first temple), but it seems very unlikely that it’ll require us to even know about the unity.

My guess is that one of the DLCs will be about House Va’ruun and take us to Va’ruun’kai.