I would be in favor of a deterioration time tax on loot. For example let say you've acquired a elite sword, I would give that sword a deterioration time on basis of how often its used and how long it's been in your possession. I would allow games to keep the sword (skin) but the combat value would be nil once it had met it's deterioration criteria.

I also would be in favor of a non-playing tax. Basically charging players gold who don't log in and play a set amount of hours. The tax would be based on amount gold in your possession. More gold a steeper non-playing tax.

Of course there are loopholes for these such players spreading their gold/items across multiple accounts/players, but that can be curbed by limiting transaction of items. Gold would be harder to police.