To be honest, the Flameheart story may well lead to more Legend content somewhat soon here. The pseudo hint in the game has always been the Pirate Lord's comment that one day something may come that only Pirate Legends can deal with.
We're now to the point in the story where Flameheart is directly invading the Sea of Thieves. I suspect we are drawing to the point that the Pirate Legends on the seas may need to step up and handle some things.
My guess is that we see this through some PL exclusive (meaning you need a PL in the crew to do it as normal) Tall Tale content and likely a few event things where PL will have some special side things alongside core events. I also wouldn't be surprised if this is where we start exploring the Sea of the Damned as a possible world expansion area that requires some kind of effort to get to (my guess is via the PL Hideout). I am leaning this way since Flameheart is also not physically in the Sea of Thieves right now, rather it would seem spiritually and his Armada is drawn directly from the Sea of the Damned. Plus Rare said back in the day they had more they wanted to do with this part of the world at some point.
So, that all screams potential Legend content to me. And that would truly make things feel like becoming Legend is the actual end game. After all that time on the seas watching Flameheart trying to take over you finally get the means to go after him and try to take him down. This could easily be a PL "Shores of Gold" equivalent.