I looked around the community and couldn't find any other suggestions on this, so here is mine. Feel free to comment on it.
Even though the arena was closed down and with it the purpose of The Glorious Sea Dog headquarters, it sadness me to see this place having no purpose in-game anymore. I would love to see this place turn in to something like a Pirate Heaven or maybe open up unique opportunities for new Sea Dogs adventures. Here we could for instance revisit some of the old memorable NPC characters that has been removed such as DeMarco and Lesedi and the other retired NPCs. For once, this could also maybe be a special place to buy/archive certain in-game items as well as being the only safe place for all players to meet. Although it is pretty close to the Reapers Hideout, it would only be within a certain proximity you are safe to avoid exploits. But going here would of course always be a risk ;)
This is just my thought for new suggestions.