I'm a fan of level caps for those sort of games. No matter how dedicated, there comes a point in every grinder's life where the mountain in front of them is just plain too much to climb. That's the point where they quit.
Clearly, you've never played Aardwolf MUD.
Clarification: You go up to level 200. (Individual levels aren't too long; maybe an hour once you're pretty high up there and not playing all hardcore.)
Once you reach level 200, you can remort, and become two classes at once: A level 200 fighter can become a level 1 fighter/mage.
You can continue this process for all 7(?) classes. Each remort increases your XP requirement per level by 1x: So a 3x remort needs 3x experience.
Once you have remorted into all classes, you can tier: Characters start at tier 0, and when they advance to tier 1, they are once again a level 1 single-class...but they get to assign some permanent stat-point-buy discounts, and get access to all their skills ten levels earlier and can wear equipment ten levels earlier, and probably get some bonus to-hit/damage as well. I don't remember what this does to your XP requirement.
Once you hit tier 9 and fully remort, you can still play around with shenanigans like dumping your levels into stat boosts or more HP or whatever instead.
This whole time, you can do quests every half hour, which earn you quest points that you can dump into special quest equipment. (Quests are 'This is the name of a monster, this is the area it's in; kill it within a half hour'.) You can also do a campaign every level, which usually slows down your OMG MUST LEVEL FASTER experience but breaks things up a bit. (Campaigns are a series of multiple, harder quests that you have a few hours to complete, for a large bonus. And can do in parallel with normal quests.)
For reference, if you play all the way through, and you play all hardcore and only take a half hour per level, you are gaining 14000 levels over a course of 292 days of solid play (assuming you never sleep or take a break to socialize).
There is not a shortage of tiered players. Most people who have played for even a little bit are T1 or T2 or something. Back when I still played, there were quite a few T9s.
...I want to play again. GODDAMMIT. (I only got up to my first remort. Cleric/ranger centaur I think? Yeah I got like a level per two hours. I idled a lot.)