Announce what to whom? To the hundreds of millions of users out there that don't even know what a browser is, let alone why it's now talking to them about something called a "site isolation framework"?
I would guess you would use a deprecation message in the console? Like they have done over cookie changes, etc. A normal user would obviously not check the console, but the devs or admins of the site sure might.
That's assuming there's still a dev around that has knowledge of, or even access to, the source code of a given webapp depending on the legacy functionality.
Sure. I just got a vibe from this thread that breaking security changes in the browser is a totally unknown phenomenon, but we had changes to behavior from other origin headers, demanding ssl and changes to cookies. Somehow we survived. ;)
A lot of people did complain very loudly about enforcing SSL, and it took decades to get here. Same for cookies.
So yes, breaking changes for privacy/security reasons do happen, but they're very painful, and if there's a more secure alternative (in this case, still isolating communicating processes and providing communication via IPC, and providing an opt-out way of the legacy behavior), that's often the easier path.
