I don't know... If some rule like this came in to play, I'd have to decide between the Rheinland Military and the Phantoms and delete the characters of the opposite faction. Basically, what I'm saying is, the RM might just simply disappear since most of the RM is also Helghast or Phantom. -.-
EDIT: Seems Korrd posted.
Well, it seems that the third option would be the best, except I have the problem with the above.
The second option will probably be the one taken, but it seems somewhat ill-defined. There seems to be a lot of loopholes that could be found. Does that mean if the "hostile" status changes to "war" a player must pick a side and not use the ships from the other faction until the war is over?