As we know, hidden services can be useful for all kinds of legitimate things (Pond's usage is particularly interesting), however they do also sometimes get used by botnets and other problematic things.

Tor provides exit policies to let exit relay operators restrict traffic they consider to be unwanted or abusive. In this way a kind of international group consensus emerges about what is and is not acceptable usage of Tor. For instance, SMTP out is widely restricted.

Has there been any discussion of implementing similar controls for hidden services, where relays would refuse to act as introduction points for hidden services that match certain criteria e.g. have a particular key, or whose key appears in a list downloaded occasionally via Tor itself. In this way relay operators could avoid their resources being used for establishing communication with botnet CnC servers.

Obviously such a scheme would require a protocol and client upgrade to avoid nodes building circuits to relays that then refuse to introduce.

The downside is additional complexity. The upside is potentially recruiting new relay operators.