So the trouble with making him the master codebreaker is that there are a couple pieces of dialogue you have to contend with:

Finn and Rose turning toward DJ and questioning if he can really do this or not.
Poe asks if they found the Master Codebreaker, and Finn responds: “We found… a codebreaker.”

Also, the general vibe in their meet scene is that he’s just overheard what they’re talking about, not that he should know to expect them. My original idea was for him to say something like: “I lost my plom bloom in a bet…” But that doesn’t work unless he further reveals that he’s Maz’s contact and not that he’s an opportunist. Speaking of which, if Maz’s true contact ends up betraying them, it can make her character seem untrustworthy or foolish, which is something we want to avoid since it’s never addressed in TROS.

I think the idea is definitely possible, but I’m curious how you think the plot would benefit from it? No wrong answers, I’m genuinely curious.

The one thing I’ve always wanted to tackle with TLJ is, ironically, to make Canto Bight more relevant to the finale. I’d want to have those camera droids from the prequels broadcasting the Resistance’s final stand to the galaxy. So then you could have the people at Canto Bight betting on the outcome, thus demonstrating the exact thing Rian set up with them betting on the horse races but applied to the plot. And them all losing their money when Luke shows up and prevents the FO from winning. And you’d want to end it with a shot of broom boy and the other kids looking up at the screen in admiration. This way the broom boy finale scene doesn’t completely come out of nowhere, either. It also explains how the whole galaxy comes to know Luke’s legend; the only way it works in canon is if the FO spread the story themselves (probably Hux lol).