There's some really well written lore people of the community have done that I would want to find a way to include. My own stuff and other xaela tribe lore that people have made for example, I'd love to add their names to the random last name generator to make those tribes blossom naturally. I know some moonkeeper players too with such a passion that would probably have the same desire(s).
Other than that.... "Shared" emotes. Things like ballroom dancing, fist fighting, anything that involves more than one player doing an action together like some of the open world NPC's do.