Hello. I gave it a quick once over and these are my thoughts.
I very much appreciate the ``Participants'' and ``In more detail: A menagerie of keys'' sections. I've had trouble in the past where I've been reading Tor specs and a new (or inconsistently named) key or actor is mentioned in passing. Likewise I appreciate that | was explicitly defined as concatenation, since in the current rend-spec it's left ambiguous.
A few times you mention ``consensus parameters''. I assume these are values that go in the params field of the consensus, although it wasn't particularly clear (for me) until I looked it up in dir-spec.
I like the ``Offline operation'' idea; that would certainly be more secure than distributing the same private key to several servers.
In the hsdir_index(node) formula what exactly is ``node_identity_digest''?