[Valg]

One problem with this system is that the 'best' players are simply the ones that got there first, whether or not they've been playing. Too much time-based advancement, and down the road it's a turn-off to new players who feel like they'll never be able to compete. You need to mix it with something else (like Eve does) so it doesn't turn into .

A variant system I've seen used is RL-time-capped advancement. In other words, you can only gain X experience/coins/widgets/whatever per RL day. This is usually done to appeal to the casual player at the expense of the hardcore player who spends 8 hours/day. It needn't be a hard cap, either-- you could implement a diminishing returns system so that playing past a certain point isn't useless.

A variant on the variant is to cap the number of actions a player can make in a day, much like many turn-based games. You could structure a MUD so that a character 'wakes up', gets increasingly tired as gameplay proceeds, then has to 'rest' at an inn or tavern. Recuperation could scale linearly with RL time until the character was at full strength.

These kind of designs sidestep grind. You can't set up a game where smashing 5000 goblins gains you one measly level, because it might take 6 RL months to do it. Instead, the structure of the game forces the design towards providing a few intricate challenges.