Not the parent poster but I'd say it's very realistic. I've written a few applications that target both JS (web browser) and binary (server) and it works very well. One example of this is https://picheta.me/snake/.

I'm also working on a game that I haven't quite moved to iOS/Android yet, but that is my plan. So far targeting the desktop with SDL and HTML5/Canvas with the JS backend works very well.

Sharing code between Desktop and Mobile still a bit rough. I have done some experiments and it looks promising: https://forum.nim-lang.org/t/5197

Does not appear to be any harder then sharing C or C++ libraries.