At the moment, BlueMap doesn't seem to provide an option to display in-game nicknames instead of official usernames.

Ultimately this is already entirely functional, so low priority, but it'd be nice to be able to choose to display player's nicknames if they exist.

I doubt it ever will, since that functionality varies between plugins. However, there should probably be a way to change a player's display name via the API if there isn't already.

PlaceholderAPI supports passing variables between plugins. I've done this now with DiscordSRV, but it'd be great for BlueMap to support this too.

Another option could be to have it so if you click on a player/hover over them, it shows both username and nickname