As someone who (very sporadically) maintains a couple of small open-source, cross-platform side projects, what I'd be interested in is the prospect of Windows support for the thing. Having been burned by hobbyist Windows development in the (distant) past - in my experience, once you've installed Visual Studio and necessary SDKs, a machine will never quite be the same again, and the experience for integrating with third-party libraries is (was?) horrendous - my approach to cross-platform development is "do all the work on Linux, use a build system which supports cross-compiling, cross my fingers and hope the result runs in WINE". Currently I'm toying with Meson on Fedora, and can at least get that far.
However, if you do actually use any third-party libraries, and want to ship something more complex than just a single executable, you'll want to actually take care of bundling your dependencies & check that the finished package actually runs out-of-the-box on another machine - maybe even make an installer. Even assuming you've used a good build system, and written clean code, that kind of stuff is the 1% of cross-platform development which takes 99% of the time. It's also trickier to do without actually using Windows, which makes for a frustrating combination of virtual machines and/or constant rebooting between Linux & Windows, especially when working on something alone, in your own free time.
Forgive my ignorance, but what are the chances of having, say Windows with Visual Studio, MinGW, and WiX in a Docker image to use with this?