@janneke @ekaitz_zarraga @civodul Well, I guess the first point is similar to Xorg stuff. Xorg is also MIT but we do ship in in Guix. And both are GPL-compatible, so you can take a any improvements from musl and move to meslibc.
Hurd is a more interesting point. For real baremetal bootstrap neither Hurd nor Linux kernels are good anyway, you need something far simpler. But for userspace only bootstrap (as in Guix) that's definitely a valid point.