Sidequests are already a bit too much like what you proposed, but maybe I misunderstood.

I think leves (when expanded) will make for a good source of primary progression, along with improved Behests. However, they leave something to be desired for solo players, even though you can still mob grind.

To deal with this, dynamic content should do. It doesn't have to be as complex as in Rift, but it should be a good means to gain skill alone (while fighting with others). It is a way to complement the existing systems, in other words. [If they haven't scrapped Hamlet defense battles, that's a good way to accomplish this.]

Since DoL doesn't get as much out of leves as the combat classes, they can be included in this activity.