It does make sense to require that a single kernel can work on all
possible hardware. So if we remove sun4m/sun4d support, all that
is left is LEON, and you likely wouldn't need to worry about other
CPUs any more.
However, there is still the question whether a single kernel needs
to work on LEON both with and without CASA. Do you still care
about Linux users on LEON cores that do not support CASA, or is
widespread enough that you just make it unconditional for both
SMP and non-SMP?
I hope that you can make it to 5.10 then, as this contains the work
I did for 64-bit time_t, which is required if you have users that want to
run systems after 2038.
FWIW, glibc-2.31 does not have support for 64-bit time_t yet, but I
know there was interest in adding sparc support to the musl libc, which
does support 64-bit time_t.