So I find and research the 6 precursor civs. That gives me a clue to there home planet. Fly my ass over then scan system and nothing. Nothing to research. I still have quest sitting in my situations log.
All five precursor homeworld will eventually be discovered (spawned) in galaxy, as empires slowly complete their artifact quests. Once a homeworld is spawned, it is an open race for everyone, if it is in neutral territory.
If it is inside border of any empire, though, it will be available to that empire only. And that empire could also lose the chance, if it is somehow prevented to survey the home planet. When an empire gets the reward (really small by that time usually), in most cases all other empires that have the same quest don't receive notification telling them failed, so their quest lingers in situation log forever. And worse, if an empire has First League / Irassian / Cybrex artifact quest and it didn't manage to complete it first in galaxy, the quest will be unfinishable even when it gets 6/6 artifacts and beyond that.
Yes, the precursor quests are that broken right now. I fully recommend using some precursor fix mod, such as my mod.