It seems to me that apart from in the guide and polls, far from maintaining a "hard distinction", DPC has deliberately and repeatedly blurred the line between the two categories when it comes to the game/story content itself. Quinn, for example, has had her own prologue, her own hangout, her own path, and her own animation at the end of episode 8.
As you say, there's no debate that DPC places Quinn as a SG. Yes, Quinn is undoubtedly the most prominent SG. As something of an antagonist, her role across the story is more significant than any other SG. That makes her special among the SGs, fully deserving of extra attention in the 0.8 others end scene.
In fact, as a result of all this, it's not uncommon for new players to say they assumed Quinn was a Main Girl, based on their experience of the game. This happens so frequently that at a certain point I think you have to accept those players are responding to something real in the game, in terms of the way Quinn's character has been purposefully developed.
Or it just means players new & old struggle with the idea of their MC getting close to characters they ultimately can't 'get' in the end. DPC wants you to care about all of his characters, that doesn't mean they're all destined to be romantic interests. Some people pine after Riona or Jade too. Fling vs love.
Just a quick word on your reference to RP: I think I'm right in saying that DPC has spoken about moving away from this as being a big determiner of relationships. There are a few examples of where it matters, in very minor ways, in the first 8 episodes, but mostly it doesn't. So I don't think we can be confident that lack of RP means no ending or relationship with a SG.
DPC is still doling out RP points in Ep 0.8, but yes I don't think they're a big determiner of relationship. I see them more as an indicator of the depth of the relationship (romantic or otherwise, Derek has RPs too). Other things like affinity or key events mostly determine if you're on the path of a given MG, which is also the case with SGs. It was more an example of an explicit distinction between MGs & SGs in game which has been in place throughout development.
But in my view, this is a comment about the way the main story is structured, it doesn't have anything to say about the viability of the romantic options. Quinn is not an MG (so far), but she is definitely a LI. I think DPC has made this pretty clear.
Conversely I suggest DPC doesn't use the term LI, he only refers to MGs for those who have romance paths. So I think DPC has made it pretty clear none of the SGs are LIs. Hopefully we'll get some indication of where the Zoey thing is going soon at least.
I'd be willing to bet Maya and Josy will eventually get solo paths. So why not Quinn or Zoey, too?
I'd welcome the solo paths for Maya & Josy, if that eventuates. The distinction is obvious though, DPC labelled Maya & Josy MGs from the start, and the others SGs.
It's not just that they're half naked, it's that the discussion started because they were looking at each other in bed. Moreover, Bella knocked her wedding photo off the stand once Jill left, clearly linking something about the topic to her failed marriage. As I said, to me the implication is obvious. But as established, DPC likes to mislead us. So I say it's too obvious.
How is looking at each other suggestive of any intimate relationship? It's not like there was smouldering sexual tension in their gaze, if anything Bella looks cross & Jill looks pensive while she's thinking about broaching the topic they argue about. Yes Bella knocked the photo over, because she was upset about Jill bringing up 'it', and annoyed at herself about lashing out at Jill. What's that got to do with Bella/Jill having been intimate at any stage? If anything the photo thing suggests 'it' is about James disappearance. Yes I know people have suggested a Bella/Jill fling being related to James disappearance, but again that's completely unsubstantiated fan fiction. There's nothing in that scene to support Bella & Jill were ever intimate. But it would be hot if they were...
Does anyone know if this Bella bedroom scene changes dramatically if either Bella or Jill are not romantically interested in MC?
It does not, no switches at all in that scene.