An Island management mod is needed to manage the community server. FTB Team Islands could be a valid option.

The mod must be capable of handling structures bigger than 32x32x32 (max .nbt structure size).

It must also be checked whether a server only mod is sufficient or if it must be present in the client too.

If no such mod can be found we could try doing this via world edit.

We (mainly @voruti and me) discussed this topic in #craftblock on discord and tested a few things.
Here our results:

Void Island Control / FTB Team Islands

Both mods allow generating a new island when he runs a command. The island must be provided as .nbt files.

• MCEdit or Recurrent Complex could be used to create .nbt files bigger than 32x32x32
• Ladders, torches, Beds, crops, ... will pop of when the world generates
• huge lag spike (5s with intel core i9 cpu!) when generating the island
• modded blocks did not generate if .nbt was created with MCEdit

Pre-Generated world

We can just copy the region files to generate new islands. This will make them appear 32 chunks (512 Blocks) apart which is quite a good distance. To save some work this python script may be used:

import shutil
for x in range(0, 16):
    for y in range(0, 16):
        if x!=0 or y!=0:
            shutil.copyfile("r.0.0.mca", f"r.{x}.{y}.mca")

This test created a world with 256 islands. The world was about 1.8 GB big. The script can easily be adapted for more islands.
Here ist the created world: 📁 template.7z

We would need some command block or open computers setup to teleport new players to an island.