With this simple idea being based on the original 4 Pillar survival design, Multi-Pillar Survival will have many realms to work with as there is gonna be more than the original 8 available.
The new realms will be as follows:


Atlantis (Maybe will be changed to the underwater realm)
Sandland (the deserted tower plain that will have a desert theme, will be the only place to get sand and acacia trees)
Middle Earth (The area of dirt, stone, ores, clay, and a different tree per tower, will be the starter realm)
Mushroom
Kingdom (the only e tower area that will have 2 mushroom-based towers
and a mycelium tower, Will be the only place to find the mooshroom egg
trades)
Netherrealm (the only place you can access via a nether portal, fortresses will spawn but quite far away)
(edit 1:) Ooh, I forgot to mention there should be an end city added and I will have it accessible via original ways.

And since this is gonna be a 1.13 map, there will be data packs allowing
for realm portals, there may be either portal shards or on spawn island,
there will be a portal spot where you can set it up. (I am undecided if
you may be able to just make nether portals and throw a special item at
it to turn it into a realm portal)




And as I said way above, this is just only an idea and I need help to make this possible as I am not good at making data packs but, I can make the pillars and the realm designs. (I will need this build on a server to save time making the data pack work with the format of the realms)