(there are two 5)'s above but i'll refer to the first one)
 i vote for the 5) auto-start strategy. user selects which one he/she
 prefers. the default should be "classic" and i would add fallback to
 "d-bus" and/or "osc" whatever. i still fail to see the problem of
 honoring
 .jackdrc if it exists on your home directory. ie. if .jackdrc exists
 then
 do the "classic" auto-start; if not, check d-bus service; etc.
 byee
 --
 rncbc aka Rui Nuno Capela
 rncbc(a)rncbc.org 
But since some applications like Qjackctl or Ardour write  this
".jackdrc" file in a possible hidden way for the average user, then
the system possibly goes back in the "classic" auto-start strategy,
without any knowledge of that.
Stephane