I'd imagine each of our races has one, because all 3 of your suggestions make sense in light if recent info. That horse sound at the end of "End of an Era" when Louisoix smiles implies to me that Odin appeared and slapped Bahamut out of the sky

Also Louisoix is supposed to be alive or at least possible to see him again in ARR based on some Reinhart translations from yesterday

Unfortunately most of the summons we're aware of seem claimed by beastmen so I don't know who would represent Roegadyn. I was going to say Leviathan (sp?) bit Sahagin seem to have him claimed