Posted this ages ago, but i've been talking about this with quite a lot of people and all like the idea:

Create a world with a monthly subscription fee ($10 or whatever) but no gold/coining.

This would re-create the early game experience but at the fairly low-paced speed the game was originally designed for. You'd probably have to tune down the event rewards substantially and increase them gradually again as the world gets older.

The upside would be a well-defined fixed income from that world. Subscribers leaving or entering the world would be a clear indication on how well received any changes are.

This business model would introduce some stability, both in-game but also in the paying customer base.

So far I've met no one who had anything bad to say about this idea. We all know how addictive this game is so a free first month would probably get a whole bunch of subrscibers hooked up right away