I think this is a cool idea! But I disagree with your direction. Lets say you do rework everything to be web assembly and not bound to BYOND. I'm sure the 300 people that play SS13 would love it. But I don't think that goes far enough, for the effort required.

I think rebuilding SS13 in unity would overall be a great idea, but there is the problem of how complex SS13 is that would need to be worked. But I think with the right baby steps and SOLID design, it could be done.

But I do feel like any effort to rebuild would not be a huge success. SS13 is fun, but comparatively niche. Though as a mobile game there's a huge market.