It's an interesting suggestion. I did an internship in Canada's federal government for a while. It's definitely the case that civil servants hoard institutional knowledge for 'job security'. Even if it were legal and publicly endorsed, periodically purging the 'deep state' would be hard. Public insitutions would definitely not just be inconvenienced the way a public sector company is inconvenienced by staff turnover. They'd break and need to be rebuilt - not that that isn't the case now.

With AI getting better and better at processing natural language, I suspect one could automate a huge portion of what the civil service does and thereby make it easier for a political newcomer to replace the relatively smaller number of people managing the machines. Not sure how we'd get there though.

Term limits for staff would be even more effective than term limits for politicians.