Add an uber similar like Grandmaster Halls from PoE, with requirement to donate certain amount.
It will spawn:
1. Random player avatar (Im not sure if you can make player base enemy based on certain armor setup)
2. Skill designed by player (usually just pick from current skill pool)
3. Need certain threshold for donation (like 20 USD some sort)
It will be good for server, additionally you can create external database for monster to spawn here.
Then add something like "each 20USD donation is just for appearance of 3 months on live server".
MOAR MONEY FOR TSW!
*except Im not rich enough to donate every month for that