[bschne]

> A problem with the system of having a domain as a username is that people can claim it who don’t have access to that username. For example, someone was able to get the AWS S3 domain as their handle!

That isn't necessarily an issue with using a domain as a username, it was only possible because you could verify ownership by putting something in a subdirectory they defined which was available as an S3 bucket name (see https://news.ycombinator.com/item?id=35820815). If you allow verification only from the root directory or via DNS records this shouldn't be a problem AFAICT.