aka zero latency + 100% clientside
sorry for the bump but I had an idea
what if the loophole was that the carried player doesn't actually get picked up? they simply disappear, and their screen follows the carrying player. Meanwhile, the carrying player just holds an NPC with attributes set to look like the player being carried - a bush that looks like a player, really. Then, when they throw/drop them, the carried player get warped to the target location and becomes visible again, while the dummy disappears.
now, there still might be delay for the screen of the player being carried, having to follow the carrying player. but unlike on un, the rest of the server won't see it as the carried player warping around behind the carrying player, since the actual carried player isn't the object being carried, but an invisible character tied to the carrying player's xy