It seems like an /etc/gss/mech.d/README-<arch>-<soname> (or similar) would alleviate the technical problems with having a single file named README, and would be glob-able for consuming software that is adapted to know about a broader convention. It would, of course, be slightly confusing to users even if there is only one file with such a naming scheme, let alone two with identical contents.
Would such a scheme be preferable to removing the README entirely for buster? -Ben