Make it an option.  Enable it by default if you must, but there are those
   of us who would prefer to run it "the old way".  A run-time check would
   be the best way to go.

i agree with this. how about you just ask the user at
install time if they want "system V init.d" or "bsd /etc/rc"
(or something..).  if they choose bsd, then you get what we
currently use.  if they choose sysV, /etc/rc does the job of
running the things in /etc/init.d for you.

all that needs to be done is our current /etc/rc to become
a generated file from what the default /etc/init.d has in
it.  we can distribute this in /usr/share/rc, or something
like that (possibly as /usr/share/rc/{rc,init.c}).