unicorn OID attributes (no values) SHOULD always be placed in extensionRequest

[mcr]

Yet IMO the new approach is more adequate because there the (request for an)
extension
is in the context of the extensionRequest attribute, rather than "out of
place" in some other attr,
where its OID is harder to understand and to process without this context.
So I'd suggest stating that any such to-be-filled-in extensions SHOULD be
placed inside
the CSR attribute of type extensionRequest with an empty OCTET STRING as the
extnValue.