Do you( or any other commenter) know of any ideas to substantially increase the social incentives for teaching such that it could measurably change the turnover rate?

I would guess that being a teacher is a lot more fun if you don't have to give students grades. Especially for someone who tries to be really fair grading seems to produce a lot of unnecessary work.

As far as the system goes in Germany, I think we just pay our teachers a higher salary and we have a low turnover rate. It might be that simply paying every teacher a decent salary is the way to go.