For scenes with large numbers of display entities, it would be useful to have text display entities that aren't facing the user removed from rendering (either by not sending them or marking them as invisible perhaps?) The easiest way to check this is to get the angle between the display entity's normal vector and its angle to the player, and checking if that's within 90deg (or perhaps a bit more for large FOVs)

Problem is, that aside it adding a bit extra work on server, it would also make it more noticeable if player has bit higher ping or uses F5 to change perspective. Also worth noting that class can be extended and developer can send extra packets that attach/change it per player. Ideally would be handled as it's own separate thing. Also you should be able to set it's width and height, which should make vanilla client cull it in more cases