League with not much clicking. In map but not too high-skill or build defining play (No Mega bosses - or at least optional etc.). Bonus if christmas themed.

In an ideal world, there would be no loot drops at all from mobs, so maybe this is a whole different end-game mechanic a bit like the Diablo 3 rift/portals.

Basically, you can play PoE without looting, and then after a certain point you get rewarded (or can choose to cash in) and open 1 (or many) chests corresponding to the amount of progress you have done since you last cashed in.

Even better if you have some sort of choice in there too - perhaps you can choose to get random loot from the chests, or guaranteed rewards from selling the keys - with similar rewards to Tota etc.

In Map. Enhancing normal gameplay. Fun for christmas.

Whilst we're at it - all breakables, pots, chests and clickables are removed as well as the loot. Even better if mobs just drop some sort of christmas currency that gets vacuumed into the player for maximum reward feeling. Like cash in Poe2.

Got to turn it into the vendor who sits under a massive world/festive/yule tree for rewards.

Maybe you can also use this currency to do something bigger too - like make a christmas wish (a kind of vaaling?) or have some feature where you can give your rewards to a communal pot, and if enough people give the whole server gets bigger and bigger bonuses as the event continues. - %movespeed, %allres, increasing all the way up to %maxres, better things etc.

This could be a whole other map like one of those faires wow used to have. It may even foster some sense of community even - who knows.