It's still marketing. "Something you've done" could be the 'is-negative' repo that was briefly on the frontpage today [1], and the candidate could launch into a heart-rending speech on the virtues of modular programming. It doesn't say anything about whether they can actually program. Or "something you've done" could be an incredibly sophisticated engine and the candidate isn't good at marketing and comes off worse than the first guy, despite being a top-rate programmer.

[1] https://github.com/kevva/is-negative

You're looking for an edge case to break a hard rule.

In an actual interview, when they are talking about something they've done and explaining it, the interviewer will be able to ask more questions and hopefully (as an interviewer) have enough of a technical background to separate the BS from the skills.

If two chemists are talking to each other about chemistry, one's not going to be able to easily just make stuff up that the other blindly accepts.

Well, I guess you might be right with the chemist example, if it's an aquihire type of situation. With something like Google though, I have a feeling these kind of talks wouldn't scale well (in general any time you say the word "hopefully", that's a sign you might be relying too much on luck). Maybe whiteboards for entry level positions, and a combination of whiteboards and fireside chats for senior positions?