The title says it all, but i dont know if it will take up too much space(if so maybe add it as a plugin/module for the mod?) and if players want it.

This has already been suggested before, and you specified the main reason that I won't add, which is the size of the mod, you can create a resource pack for that yourself:
https://github.com/Wilyicaro/Legacy-Minecraft/wiki/World-Templates