I wonder if Rinko and Shu would get along, should they meet one another.
That's obviously part of the thing; yes, it's being presented as "Aya & Mitsuki need to talk to one another still, but they still love each other and aren't actively in full avoidance mode" (though Aya has been avoiding going back to their flat here and there). But they're still meeting up and they're still going out and the subconscious need for physical touch is obviously present.
But Shu & RInko are now in the storyline in substantial ways, and I suspect they'll serve as additional points of reflection for Aya and for Mitsuki in getting the Main Duo to confront one another honestly.
From there.....well, I personally would like to see Shu and Rinko find fulfillment. Ostensibly, that comes in the form of a partner, per the context of this series and it being about relationships. Shu being into Aya is less overt than Rinko being into Mitsuki, but it's basically what's being presented by the author, and they'll both have to navigate the fact that they've fallen for people who are taken, and happily so.
So that would mean they're available for one another. Of course, compatibility is important, but it would be interesting to see how the author weaves that story, provided it's part of the plan once Aya & Mitsuki are back and talking and have hashed out their various troubles and grown stronger together.
That all said - I feel Rinko in this one. I've had a similar moment in my day, and it fuckin' sucks watching someone you're crushing on run off into the arms of their committed relationship like that.
Because you know you can't say shit about it, and you know you won't, but. Yeah, it still hurts.
Anyway thanks for the TL.