I think it's a definite Maybe.
I'm definitely in both spheres - my work covers a lot of the existing questions here, as well as the sort of things the proposal covers, so I'm pretty biased towards "Yes, it's covered here".
I'm far from convinced that the proposal is a big enough community to support itself - there are a few dozen people that I know of involved in it, maybe a few hundred or a couple of thousand globally. It's a very specific niche. But new Stacks have been set up and thrive with surprising niche communities, so maybe I'm completely wrong on this. And it's not for me to second-guess.
Many of those modellers would be well placed to answer other questions here. I did try pointing the community at this site here, but I don't think any actually came. (Is there a consolation badge for being a very poor recruiter?)
And of the example questions on that proposal, the ones that really didn't have a place here, could have a place on other existing SE sites: Open Data, Scientific Computing, Cross-Validated, Data Science, GIS, Stack Overflow, etc.
I've just proposed (on the discuss.area51 question) that it would be best named "Sustainability Modelling", which does bring it very close to being a subset of what we do here.
We don't yet, AFAIK, have any techy modelling questions here, though we do cover some of the numbers and concepts.
I would love to see it succeed as a standalone site. (at the same time, I'd love to see them here, giving this site a real boost of energy, new users and new questions).
Given the absence of questions of that type here at present, then if it were my call, I'd lean towards letting it go through to commitment and seeing if it gets momentum. If worst came to worst and it went to beta but then didn't survive, I'd expect to support migrating the questions here.