It would probably be doable to run a very small Linux EFI stub as a
bootloader on x86, that way you can side-step the lacking grub support.
Integrating it with Guix would surely be a bit harder though.

kiasoc5 <kiasoc5@disroot.org> writes:

> Argon2 support was slated to be in the next release of Grub (2.12) but 
> apparently this is not realistic:

As for LUKS2 support in Grub, as long as you use PBKDF2 it should now be
supported by HEAD.

Best,
-- 
Josselin Poiret