Yeah, that was made pretty clear, and besides, an Ishgardian GC wouldn't even make sense lore-wise. Despite entry into Ishgard being granted to us, we are an exception based on a set of extraordinary circumstances rather than the rule. Ishgard isn't throwing open it's borders to everyone and anyone - they're still remaining closed off to Eorzea at large (which is the whole reason we're even in Coerthas, the Monetarists and Crystal Braves would be refused entry at every turn), and have not rejoined the Alliance, meaning no Ishgardian Grand Company.

I have no doubt as Heavensward's story progresses we will eventually return to Ul'dah and restore our reputation, but for now, we're basically turning our backs on the Alliance (or rather Ul'dah). Meaning no GC rank promotions, because we're effectively 'off the combat register' with them.