That does not really answer my question. Why does missing support for Yubikeys "suggest [that] something very very scary going on at the organization"? Supporting Yubikeys is probably already in their list of planned features. But ProtonMail is a relatively small company and the user base requesting that feature might be relatively small. Yes, security is one of their top-most priorities but so is earning money. The latter requires a large paying audience where other features might be more important.