Rev4 update

This is in sync with https://docs.google.com/document/d/1m7Cep2U5eCe5M62Y6a_4CNGF7QM4UgJtmMFq2FrRo3s/edit?usp=sharing

and implements the proposals there. Please carefully review (in particular removed messages). This will go soon in master after another community review round. Criticism now or never 8).
We believe these have been used so far mostly within ETH and people are ok to port to the new equivalents which offer more fields (below).