I always envisioned a POP auto-promotion being pretty much just that--the POPs would promote themselves when they got enough money and consumer goods. Of course, some jobs couldn't be auto-promoted into--only rather small numbers of people decide to become soldiers, for example, so the only way to get more soldier POPs would be to promote more soldiers--but most jobs could be accessed by POPs in this way.
Furthermore, I envisioned the cost of autopromotion being on a sliding scale. A farmer, for example, might need only access to life and everyday goods and an open job slot in the state (or perhaps country) before becoming a craftsman, but a clerk becoming a capitalist would need to have all needs fulfilled and have a substantial amount of cash. The difficulty a POP faces in autopromoting might even be modified by other factors, such as literacy. It would be easy for a craftsman to become a clerk in Britain or Germany, but very difficult in China or Bolivia.
This would, I think, make industrial development slower and more realistic. Instead of building a bunch of factories way out in the middle of nowhere and instantly turning a bunch of peasants into factory workers, you'd have to slowly build up your economy to allow your peasants to migrate to cities and become craftsmen and clerks. You'd have to make tough tradeoffs in the budget; do I have high tariffs to balance my budget (knowing that it slows POP development) or do I cut back on military spending, for example.