… is that really the origin of “toast” in a browsing context? I would have expected it to derive from toast in a gathering context (“a call to a gathering of people to raise their glasses and drink together in honor of a person or thing, or an instance of drinking in this way”) in that it’s an interruption of sorts.
Personally, I’m more worried that Google is going to try to slam some kind of default behavior onto that only really works for them that’s really difficult to circumvent. The casualness of the tag is, in my opinion, kind of irrelevant so long as it adequately describes the semantics. For example, I think that
aside> is pretty casual sounding, but it very accurately describes what the content is. In that vein, I would agree that is probably not the best choice; is probably better.