[pwg]

> I was also hoping that, because open <dialog> elements exist in a distinct top-level layer, that they might even able to escape the bounds of the browser viewport, which would provide real value to the end-user in a lot of places

And, within three seconds of release, a <dialog> with this ability would be misused by advertisers to bring back the old pop-up windows that all browser's block by default now, because of advertiser misuse.