But the OCSP protocol doesn't need certs. It needs a DN and two key hashes.
Why not just define an OCSP critical extension that says "verify this cert,
and verify up the chain as well." The footprint for a dedicated DER parser
that knew how to generate only those requests, and parse only well-formed
replies, would be pretty small.
Why won't that work?
As I've said earlier on this list, the OCSP protocol would have to be
rewritten to allow this. The semantics in the protocol were purposely
restricted not to do this. However, it is more than just rewriting OCSP and
having it recycle at Proposed Standard. SCVP has many features in the
request and response that give much more granularity than what you propose,
as well as other features such as passing back the information needed by a
client to validate.