What would motivate many that love mining, collecting, and combat. Is unique items. I would love to spend mining in the mining world knowing that very rarely I could find an enchanted drop that I can trade with a villager at the spawn marketplace, or perhaps use to enchant one of my favorite items with.

Having an unbreaking v pick axes, or unbreaking x gold helmet for example (keeping it simple here). Would be pretty cool.

Collecting these artifacts that are quite rare, could mean I would spend more time online mining and trying out my luck in the new mining world with my friends.

And what is that? There's a rumor once a year a villager in a boat arrives with a fortune v pickaxe for x of these rare artifacts?

But yeah, I think it would be cool to hear a bang during mining and find a super rare fossil, some ancient scroll or unique artifact we can then use to spiffy up a buff on armour, or enchantment on a tool beyond what we can normally do.

.. (just an example)

I think it is actually really fun if it is really really rare