Well one thing that can be done is to is to implement activities that would have a similar reward/time. Most MMOs seem to go to the extreme and have it so that quests give so much exp that people only quest to level and don't even bother killing NPCs outside of quests. Instead of that, since to many people that feels too linear, I'd have quests that didn't follow an overall story and had various gameplay mechanics, like, tower defense mechanics, rts mechanics, standard MMO mechanics, etc. That way it keeps things "fresh." But if it takes the average person 30 minutes to complete a mission and they gain 1000 exp, then it should take the same character about 30 minutes to gain 1000 exp just grinding mobs similar to what they'd encounter in a mission. It'd never be perfect, but as long as it's close I figure players would have choices. If they can log in for a few minutes, they might go grind a couple mobs. If they have more time, then they might want to do a mission or two.

What I'd like, and I know it'd be hard to balance, is dual advancement system. Lately I've been playing some offline sandbox games like Red Faction Guerilla and Red Dead Redemption, and one of the things I noticed is that they eschew the exp grind in favor of obtaining new equipment. I think it'd be pretty cool if there was a twitch based mmo that had a robust skilll and item systems. Instead of skills and items making your character insanely overpowered, you'd have more options with how you want to build your character because even though you'd have benefits, and increasing benefits so you feel like you are advancing, there'd also be trade-offs. You might start with a skill that makes you deal more damage with swords, but at the cost of swing slower and having no armor penetration. Then, as you level up, you'll open up skills that allow you to train into dealing extra damage with a sword, at the cost of a slower swing speed, but there would be less penalty to armor penetration. Items would work in the same way. And while things would get stronger, they wouldn't get too strong. I'd have it so that you got "stronger" by training into a different "role." You might start as a fleet swordsman, but then train into a heavy armor two-handed axe guy that can take huge damage, dish huge damage, but be slow as heck.

I figure that with a skill system like this, players could be given points to use on equipping skills while in "town." That way players can train everything on one character, but they wouldn't be able to be everything at any one time. To balance this with crafting, I'd make it so that there were a ton of craft skills and crafting was more of a mini-game, similar to fighting mobs or something.

So what I think, is that reducing the feeling of grinding, devs have to do a few things. The first is to give players different choices with how to "level" and make each choice give, as close to possible on average amongst different players, the same reward/time; have many different skills that help define what you want to do with your character, but where the skills give players more options (with trade-offs) instead of raw power; and give players many different options with regards to how they would like to equip their character at any one time to enhance their role or balance out some of their short-comings.