> However, if you browse the consensuses, you will find a lot of relays that meet the requirements above, but doesn't have HSDir.
> You will also notice that almost every relay with HSDir is also a conventional v2 directory mirror (e.g. with active DirPort).
>
> Is there any non-documented requirement, like minimum bandwidth or something?

An HSDir needs to be a V2Dir. MinUptimeHidServDirectoryV2 varies allot between the directory authorities. One needs a majority vote for the HSDir flag (or any other flag)