And I have two questions left:
   - Will those arguments to "modload" be required for all times? Or will
     this be improved if the LKM interface cleanup is done.

see below.

   - What is the use of the "ffs" LKM? For diskless NFS clients? Because
     else it could be hard to load this LKM without filesystem support.

yes.


our current LKM system is sorely in need of revamping.  perhaps we
can take some things from freebsd, but not having looked at their
changes, i can't say either way (but i hope so).

many things that would be nice to be LKM's (such as the compatability
modules) don't currently work as LKM's because of depedancies on
that code in other modules (run a grep for COMPAT_ in sys/kern/*.c
to see what i mean).

michael has suggested one way around these problems, but it wasn't
really a workable, scalable solution, IMO, and i've not seen any
others that are.  michael even created a mailing list to discuss
these ideas but unfortunately, that appears to have died.