[heavyset_go]

If you're worried about your ISP or people snooping on your traffic, then this scheme can be trivially defeated with a downgrade attack or looking at your address bar.

[antocv]

My ISP can not "be looking at your address bar", you are thinking of Google.

Downgrade attack, would not work since I use HTTPS Everywhere, and once my browser has visited the site it refused to downgrade - that header is set.