Multiplayer Servers VS 2D Farms

Many mob-based farms in Minecraft rely 2D (two-dimensional) mechanics, whereby mobs are transported from Overworld to Nether (or vice-versa) so as to remove them from the mob cap as fast as possible in order to increase the rates of the farm.

These farms have one downside though - on multiplayer servers, the instant the mobs move to another dimension, and that dimension has a second player somewhere else in that dimension, the mobs instantly despawn, as they are outside the 128-block despawn-sphere.
This limits the gameplay options of players on multiplayer servers - either they are forced to use "1D" farms, or they require a second player whose sole job is to stand on the other side of the portal to prevent the mobs despawning. 

Suggestions:

1) Mobs are given a 20s grace period (5s longer than the portal cooldown period) after entering a new dimension, during which they are protected from despawning. This could be achieved by applying the "within 24 blocks of player" tag to the mob (for 20s only).

Or

2) Mobs standing inside a portal block are protected from despawning. This 2nd suggestion would again open up gameplay options, and would come with the advantage of providing variety between single/multi player, but would come with the downside that additional effort would have to go into designing + building different versions of the "other dimension" of the farm for different playstyles - a challenge I'm sure the Technical Minecraft Community would be more than willing to take on!