Nothing more complicated than people. This is a special case. For configuration, it's dead simple. Sad reality probably says yes. If someone sends me a stable spec of X.509, I'll put it in.
Complex metadata causes protocol problems.
This may come up again. Mailboxes aren't going to cause this problem. One email address per entry. I probably want to add second email address to primary email address. The document editor has enough guidance for the next version of the draft.