Look what i found!

[Tonkyhonk]

Wasnt w4 just a placeholder world till they add the curio ( disusting! ) system?

yeah, and the reason for the curio system was botting, iirc.

[MagicManICT]

I don't know I'd call it a placeholder. World 3 got wonky with something and they wanted to add the new mining system to the game, and it was a good time. If I recall correctly, they had been working on the curio system already, but hadn't deemed it ready to go for 4. The bot mining getting extraordinary LP gains caused it to get dropped in at least a few months earlier if I understood jorb's posts correctly.