It’s not a bad plan, and certainly keeps professional politicians from getting into office in a safe district where they will basically legislate until they’re carried out in a box.
My only objection to a specific hard cap is that institutional knowledge is a real thing, and generally a good thing. 8 years would mean that the institutional average length of service would gradually approach 4 years, which would limit the reservoir of institutional knowledge.
Make no mistake: If I had to choose between the current scheme and the one you’ve offered, I’d take yours in an instant!
Edit to add: You and @dacree seem to have pretty much the same idea.