https://github.com/calamares/calamares/issues/964
/etc/default/useradd comes from passwd package and I really really really do not think we should change that! We also can't really twiddle this in a cala hook as that'd then cause dpkg config file conflict nonesense further down the line.
So, the only reasonable options are
a) intercept useradd exec and inject args
b) patch cala
c) divert etc/default (which suffers from much the same complications as forking passwd as a whole)
Until upstream says something I'll go with b to unbreak crap as the entire QA set fails now -.-