This need to be someone that truly cares about a desktop experience, and backwards compability, like Linus cares for the ABI for Linux.
The only people doing anything remotely like this is Elementary, but it is very far from reaching any kind of critical mass. Also that its perceived as macOS clone hurts it.
I think if this ever happens it will be a company doing this, and it won't contain any kind of Qt, GTK, GNOME, KDE. Perhaps one of the big ones that currently lack a desktop platform. Lets hope is is free software.