I can see Jingi's side plot + motivations coming full circle to collide with his feelings for MI.
(Ch 81 spoilers)
Now that HJ is away in the med ward MI is in danger of being targeted by the uncle so JG has to protect him. In doing so I can see both of them growing closer and JG becoming the ML.
I'm so invested too lol I have too many theories on where this could go
I think you're right about that. We might see some development between them soon, since the author's been dropping hints in the story like Heonjae noticing Myeong-il becoming conscious of Jingi, and Jingi's blush this chapter lol.
Making theories here is really fun because there's a pay off. I remember when readers on twt we're saying that Jingi was sexually assaulted by his uncle, and that ended up being true. As traumatizing as it was, it's amazing how the author has been sprinkling important details even from the earliest chapters.
As much as I hate reading love triangles as they are being serialized, I cannot marinate this for the life of me ( ̄∇ ̄")

So far, the brothers stories have been playing out quite differently. Jingi's storyline had been about their evil uncle and how he wants to stop him, while Heonjae's development had been mostly about his feelings for Myeong-il and wanting to be together after they are out of prison. If this isn't gonna have a 3p ending, I can see Heonjae being the male lead. Maybe I'm wrong tho, I kinda prefer Jingi, but the motivation of his character isn't really centered around the love triangle. It's like he has a whole side plot of his own, which I don't mind, if anything I wish we can see more of it. I want that uncle to SUFFER.