I like Avu's sugestion a lot. Peasant specs that give task performance buffs but don't affect LP/replacement.
If classes of any sort were developed it should be to primarily affect the cost of combat development for specific types of combat toons so that overall GvG were to be balanced. Stuff like Siege mechanics and wall buffs creating a long enough delay and city wide alert should be more than enough to let people log out their high investment crafting toons to meet the attacking party with combat toons.