If the new requirements are a dealbreaker for anyone, Mineclonia is a lightweight open-source alternative that runs on much weaker hardware and feels close to Minecraft.
My 13-year old son has an absolute blast writing mods for mineclonia with Gemini. He's later e on Diablo-style randomization of weapon drops, rune combinations that cast spells and have effects. And he's even working on what he calls an MMO, but really a server with quests and groups and classes, but probably wouldn't support more than about 16 players.
Mineclonia is the 'game' that loads into Luanti (formerly Minetest). Luanti has a c++ core engine, but definition of the worlds, rules, games, interactions is all lua
Yes, the engine handles shaders, networking, DBMS backends (Sqlite, Postgres,... to store "worlds"), entities (mobs/items/vehicles...) to name the obvious things, but the logic of the game (weather, mob AI, user/world interaction, inventories, forms and other dialog box, custom world generation) and other other functions (area protections in multiplayer, account management, chat moderation, ...) are done with Lua 5.1 JIT generally.
The API also gives access to things like image saturation, light intensity, strength of volumetric lighting/bloom/exposure, fog distance, so you can enhance weather effects by altering them - per player; OTOH, rain/snow has to be done with particle spawners by weather mods, and figuring out if the player is inside a building, under cover, or outside in the open is difficult.
One can also hook it with external services, e.g. instant messaging.
I didn't mean to make it seem small. I interpreted the comment as being surprised that it is written in a scripting language but Lua is no slouch, especially when the most performance sensitive code is C++. It's a very common pattern in games to boost iteration times - even the Unity engine does something similar.
Great platform for hacking.