Yes, Shells, I think Koppelman would write the movie as he is still a die hard poker fan (why he conceived Rounders in the first place, of course). I have listened to his interview podcasts over the years and the issue of poker comes up with some regularity. Let's also not forget that Damon is a poker fan too (hence my note above re Norton and Damon might be interested for the hell of it).
I think what made the movie really tick in the first place was the direction and cinematography- as John Dahl has stayed more in television since Rounders, he should be a get and I presume interested. Yet another thing to consider is Molly's Game took US$60 million domestic and international at the box office (with a production budget of US$30 million)- and that was definitely a niche movie.
However, this is where I am with you I think Shells, and those who are underwhelmed at the prospect. It could get financed and made, and everyone enjoy a nice pay day- if not in Hollywood blockbuster terms, certainly in real world terms. But, does the movie lend itself to a sequel? I am not sure it does so and I would hate to see a Rounders 2 that felt contrived, a step too far.