Just me or Els is the dev favorite LI.
Elspeth is definitely the favourite for the majority of the game's fanbase from what I've seen/read, so it would make sense if the dev felt the same way, or at least was influenced by that popularity. Still, the other girls do have a significant number of fans as well, and I don't feel like they have been given short shrift in the story by any means. All of the characters have important scenes, dialogue, and sexual interactions with MC that make sense and fit with both their personalities and their relationships to him.
yeaah I don't see Els as anything but solo path, same for most girls, except as you mentioned Vi/Ines, it's within the realm of possibility. Anyway, I like them all, so I'll go through all the endings regardless.
Els and "Exclusive" is the easiest way I find to say this, because of the similarity of the letters involved, and it's an attitude that fits perfectly with both her and the MC when he is with her. Who needs anything more than Els in their life?
I do think Amrit is also a strong possibility for a non-solo path, based on how much she idolizes and adores Kana. Also, the way she gropes Els is suggestive that something more might happen there. Plus, from a variable standpoint, she's the one with the highest possible "interested in other girls" score of all the characters IIRC, so I suspect there may be more to come with her as regards some potential multiple girl pairings.
And this doesn't have to mean "non-solo" to the extent that polyamory is involved either. A simple casual "threesome" with another woman is actually the most common fantasy for most married couples (both men
and women) from what I recall of research and surveys about the subject. So while most people don't act on that fantasy in the real world for obvious practical reasons, I think fiction can be a safe and fun opportunity to portray and enjoy that particular sexual activity.