I'll do what we do off camera!

Rhett when Rhett's telling Link to eat poison at least 4 times in one outing:

Rhett when Link's telling Link to eat poison:

I feel like it would be more like it was always there for both of them but repressed and suppressed by the culture and upbringing. I mean they've been an "old married couple" type friendship since way before I think it could even be plausible for anything to have happened. My least vibes based light headcanon is that it's similar to how they fell for Alicia (who I believe is representative of the things their upbringing tried to stamp out of them) in the lost causes of bleak creek - Rex notices some things he finds attractive and decides he has a crush, which he tells Leif, who has been crushing HARD, like imagining their life together, for quite a while. Leif's mad about this, but holds onto it and doesn't share it until later. More vibes based, I can see "Link falling harder" in the sense that I don't think he would be happy to settle with going backwards. Like in that whole email situation, Link was getting unhappy with how they weren't spending time together outside of work any more, and felt that they were acting friendship for the show, while Rhett saw it as still doing the thing they loved together and that being adequate for maintaining their relationship. I feel like if they did come out they would probably try to tell the story in some media creation. Their relationship is their muse for almost every thing they create now which is a beautiful thing no matter what the nature of it truly is.