I'm going to speak as an old SCRA player. The Sol Coalition is officially deceased, the S.C.R.A. or Sirius Coalition only survives due to the saboteurs that snuck aboard the Hispania and agents on-board the Rheinland & Bretonia. The Coalition Government maintains the illusion to it's citizenship that the Sol Coalition still exists but it too far at the moment to aid their struggle so the Sirius Coalition must 'Pave the Way' as it were for the Sol Coalition to take over once the SC have completed their mission.
The High Command of the Sirius Coalition knows that Sol has gone byebye due to Grand Admiral McIntosh's expedition to Sol years ago and are keeping it hush-hush from the population of Omega-52 until they can determine a good time to release the information that wouldn't harm the Coalition's morale too much.
I do not know if there are surviving pockets of Coalitioners still living in Sol underground in asteroids or the hulks of dead worlds, but I wouldn't discount the possibility for such RP by both ambitious Roleplayers or Devs. In the meantime however until such an ambitious person comes forth the Sirius Coalition are the only REAL Coalition threat in Sirius.
In the meantime however until such an ambitious person comes forth the Sirius Coalition are the only REAL Coalition threat in Sirius.