For a while now I’ve used the XPKeeper Bukkit plugin by eccentric_nz on my multiplayer Minecraft worlds to provide some form of “XP banking”.
I’m now in the process of replacing XPKeeper with my own xpbank data pack which I’ve written as a replacement capable of functioning with a vanilla Minecraft server. It’s been an interesting foray into data pack creation as a form of programming within the bounds of the vanilla game.