IIRC that is what some companies are already doing - they don't have enough experienced people, so when they "retire" (by reaching the company's retirement age) they get rehired as a part-timer for like 1/4 of the money (while doing 60% of the work).

I actually feel that the birthrate is a huge problem here that isn't anywhere near being solved. Women want to have more kids but they don't want to give up their jobs. Even then, there's a ton of pressure to give up their job when they have kids. Also, if their husband is a seishain, there's the possibility that he'll get transferred, which requires the family to either live separately (happens a fair bit) or quit and move to the new place.

Sooner or later, the 2 tiered system of seishain and hourly workers is going to break up.