If cities produced enough shmuckers to sustain a side, a bubble kingdom would be workable.
Perhaps a bubble kingdom really is workable in theory, but in practice no one does what would be necessary to keep it going. Maybe if you spend all your shmuckers on only upkeep and pop only the units that you can use to improve your upkeep situation then you can manage a very modest little self-sufficient Erfworld life. It would mean that the ruler personally manages the capital and there are no soldiers guarding the walls. All of your units are mining, or perhaps boosting the productivity of farms, or similar things. Faq's problem might have been that they had too many luxuries: too many casters, too much tea.
Another source of shmuckers might be barbarians. We don't understand the details of when or how barbarians pop, but perhaps if a city site is left alone in the wild for long enough a barbarian city has a chance of popping, then it can be captured and razed for shmuckers.