I'd defer to the development spread sheet Aet is refering too. The development team is the group that actually dictates this type of thing. While Alvin may have a point regarding its usage, you can't ignore it because it says something you don't like. The development team made the spreadsheet for a reason - it is a guide for them. They aren't going to throw it out on a whim due to a single event. If Rheinland was to go belly up - I'd wager it would be done over a period of time in which events caused them to drop ranks on that spreadsheet until they were at a point in which it would be logical for them to be made belly up.
While I love the SCRA, I have to agree with Aet. I see zero lore from the developmnt team that indicates the SCRA could challenge any of the house militaries. Of course, in game actions do contradict lore and that is why most in game PvP stuff isn't acknowledged in lore. That is because I could take a Zoner cap ship and claim New York if I wanted. :crazy:
As for Zoners? Sure we may be able to mount an effective defense of a station that has cap ships defending it. Won't be able to defend them all though. To spread out and the house militaries are stronger.