that would be possible now, if:
   [...]

(3) PS_STRINGS was the same for all the m68k ports, which it's not.
(4) the kernels were loaded at the same addresses, so that kernel-related
    utilities that need it are portable.
(5) the ports handled the 68040 similarly, so that libkvm didn't need
    #if's.

There are probably other problems, too.

BTW, running 4k executables on a 8k machine only needs to be a *tiny*
bit less efficient that running 8k executables, even in the worst case.
I've already discussed why this is so.

Also, the 4k compatibility code *has* to be written, in order to run old
4.4BSD and NetBSD executables on the hp300.  Once that's done, there's
hardly any reason to switch the hp300 port, until the other problems are
resolved.