NIP-66 requires another relay to be able to retrieve informations regarding availability of an relays, or publishing your relay availability.

As it needs another relay to power it up, It was really out of my goal in bostr2.

The reason for that is because an unmanageable list of relays that just keeps adding in memory and never shrunk in memory gives an even bigger consequences on server side. Even it's possible to automatically shrunk it down, The reliability on obtaining information is completely unguaranteed.