The videos are only of interest to family and friends. That said, I've seen a few stats of top-page HN links generating 10,000 or more unexpected visitors, and

The videos are only of interest to family and friends. That said, I've seen a few stats of top-page HN links generating 10,000 or more unexpected visitors, and a 1TB cap with a 20MB video would easily handle that. But if that weren't the case, if I were making professional videos intended for a mass audience, then I would just add more servers with appropriate bandwidth. Scaling for your own content is vastly different and easier than scaling for everyone's a la Youtube or imgur.