I wasn't clear, but I meant "opt-in" in the sense that it would be enabled on the client by optional configuration, with big warnings for users on "corporate networks". This would draw attention to the issue, because every time a version bumped the web would be flooded with "be sure and opt in to the TLS upgrade,
unless you're on a shitty BlueCoat network!" advice. Eventually BlueCoat would get the message.
I understand that proper network hosts will negotiate TLS versions rather than "freaking out".