Corsairs and GC would never ally. Neither would Order and Core.
The big problem with Gallia is that 99% of all factions on disco were at one point or another forced to shoot mustache-twirling villains because they were at their core, indefensible morally, ideologically and practically. There was no reason to ever ally with the Royalists unless you were a Royalist yourself. This would only set the same precedence with entirety of server fighting another very limited playerbase. Nomads also never were powerful enough to take on Houses directly. Their primary strategem is subversion, not revealing their cards at the same time for all of the Sirians to bundle up and make them extinct in a single swoop of galactic super-hammer. Humans DO ountnumber Nomads and their only saving grace is that humanity is not unified.