I was under the impression the path split is more just for an optional romance / lewd scene and wouldn't really mean that many extra renders unless all of them are included in an update.
Oh no no no ... The paths as of now will completely change the way Ashe acts and reacts to situations.
It will change the story and the scenes by a longshot.
Dom/Sub/Cuck ( siren or those others ) will have a huge influence how the story plays out, otherwise it wouldn't make sense.
Main story is pretty much a Duplo who might get exposed in future updates - this will require the least amount of renders.
But the core is still Ashe trying to deal with her sexuality as a Duplo, which will be largely influenced by the path the player took!
So as i see it most of the LI's are bound to the different paths, you have a little preview in the dream sequence.
Lexi as example seems like a LI only available in the Dom (Siren) path, Natasha on the otherhand is only available in the Sub path.
But saying that, the question is who do you see as a optional romance ?
I mean the Mom or Rachel are they optional or main LI's ?
Storywise i would say Mom and Rachel are actually main LI's so yeah (this won't be the fact if you go the cuck route as i see it ).
So no i don't think optional romance / lewd scenes are really a thing, because we don't really have defined main LI's in the game (beside those i mentioned).