My only concern with this idea is that a class-specific system makes it hard on some of the more specialized classes to solo. This is why I believe they tried the multiple-class abilities approach, but I think we all realized that it takes too much away from enjoying the job you're playing and made leveling into a giant ability grab. All I am wondering is if anybody has ideas on how to make Kuro's system more enjoyable/easier for solo players?

One of my initial thoughts was to just encourage duo play rather than to keep the emphasis on solo play. I feel like duos are easy to create for casual players and they encourage making friends, which is what develops a strong MMO community.
SP/EXP rewards from quests. Anything that you do on your class should reward you with progress to your class. Again, it works in every other solo-grind-to-top MMO.. With proper execution it will work here. lol

Some of the base class skills can be used across the spec. So say for a CON/WHM soloing they would have low tiered elemental nukes (Fire, Blizzard, etc) and their higher level offensive spells (Holy, Banish anything else they could come up with).