something like this has been suggested quite a few times before... but...

rather than shoot down this idea... i think i could lend a suggestion that might make it more possible...

rather than give them to players at the start of the game... (kinda would mess up with new crews joining & server merging)

have "capturable locations"... something like sea forts, but new...
(they can't be existing seaforts or skullforts because that would conflict with dive voyages and world events)

each crew or alliance can only claim one at a time...

you'd have to capture it from some enemies and also hold it against waves of enemies, with a boss...

and then the location would be marked on the map with your chosen cosmetic flair..

when you capture it, all of your applied cosmetics would be added to it as well; cannons, rugs, curtains, tables, lanterns, trinkets and stuff.

there would have to also be a well balanced high-risk to high-reward for stashing loot...

maybe a claimed fortress could be manned by a npc skeleton crew... that could also be customized...

idk... if Rare is considering something like this,
considering how many times people have asked for it,
they'd have to design it well, and it would have to serve a new purpose... not just another "emissary flag mechanic"