Some sort of protection against thievery would be nice aswell. I know it didn't happen often, but as I heard it did happen. Map of the server, Some sort of resource world/area for gathering materials to prevent the destuction of the original landscape, personal portals, some way (not neccessarily easy or quick way) to obtain hard to find and not replenishable items (such as saddles, shulker boxes, elytras etc.) was mentioned on Discord aswell earlier I think.
If a lot of animals cause the lags, a solution could be an animal farm which had lots of spawn eggs of different animals (not accessible to players, so they can't take them), so if people wanted to let's say kill a hundred cows, they wouldn't have to have a them loaded in all the time or breed them endlessly, but just go to the place, spawn the cows and kill them. This would probably make the gaming experience worse for some players as this method of obtaining items or experience might be the most efficient, but it can be quite boring aswell in my opinion.
I asked on TS if people wanted to add some other things.
Atreyu and Stormmy mentioned the Twilight Forest mod and Mystcraft would be a nice touch once the update hits and the lag is stable enough for them.
For now these are the things I could gather. Thanks for the thread!