Secure Boot will start GRUB 2 if it is signed. It is the approach followed by
Fedora.
Replacing GRUB because it is GPLv3 does not make sense: the Tivoization
clause of the GPLv3 would *not* force Canonical to release its private key.
It would force the hardware manufacturer to allow the installation of a
user-signed key and/or to allow to disable Secure Boot. Without that and with
a BSD-license bootloader, the freedom to modify it is moot: the user is then
unable to run the modified version.
This essential piece of information (about Canonical being wrong about the
GPLv3) is, in the article you link, quite far away and hidden in a bunch of
useless hypotheses about why Canonical, influenced by Dell, might have chosen
to not contact the FSF. The FSF analysis and its recommendations make a far
more interesting reading.
