You can already implement this using the Upgrade-Insecure-Requests header[1]. Servers just need to check for that header and only send an HTTPS redirect if it's included. All major browsers already send that header except Internet Explorer so the security impact of such a check would be pretty minimal.

The only argument I can see against it is that it's insecure-by-default, but you could theoretically fix that by allowing clients to send `Upgrade-Insecure-Requests: 0` to explicitly indicate that they don't want to be redirected.

[1]: https://developer.mozilla.org/en-US/docs/Web/HTTP/Headers/Up...