> IETF wants a working open source implementation before standardising.

I don't think that's IETF policy. Individual IETF working groups decide whether to request publication of an RFC, and the availability of open source implementations is a strong argument in favour of publication, but not a hard requirement.

If the IETF standards are sometimes useful, it's more a matter of culture than of policy.

A great example of this was PKIX, whose policy was "we'll publish it as a standard and someone else will have to figure out how to make it work". There are 20-year-old standards-track PKIX documents that have no known implementations.