A vast majority of Android users know nothing about custom ROMs.

However I would say that among those who do know, Lineage OS has a fairly good reputation for quality. You wouldn't be targeting mass adoption with this, you'd be targeting the influencers.

I never heard of it before, and this about page isn't exactly helping:

https://lineageos.org/about/

I bet all the OEM manufactures do. Its not that they care at all about users installing custom ROMs. They will be looking for options to not be tied to Google forever (assuming they have looked at the history of IBM and Microsoft). The problem is they never have to actually release a Lineage OS/Tizen/${insert other phone OS here} they just need a viable option for what they would use instead when they talk to Google about licensing (E.g. Samsung and Tizen).

Fork/Successor to Cyanogen would probably net slightly more recognition.