Binaries currently work on the system you compiled on and any later release of macOS.  That's the only "promise" there currently is.

Anything better requires work, and hence someone willing to do that work. 

I'd love to be able to build on the latest macOS and deploy to older versions, but that's functionality I don't need myself at the moment which means this does not have priority for me. 

BTW. I haven't checked yet how invasive supporting weak linking for these symbols will be. That depends on where the symbols are used.