Great job, @timcliff. (I tried to write something more than "nice post!" ;-) ) I can't find any significant disagreements here so I could basically do a Ctrl+C, Ctrl+V to get a decent draft of approval standards. ;-)

Testing is a team effort.

I would like to point out, that witnesses are ... just witnesses.

Yes, witnesses play a very important roles here, however, we are nothing without those who vote for us.
Feedback from stakeholders is very important. Yes. Before the Hardfork.
Also, websites/tools providers should timely upgrade software to support upcoming changes and let us and developers know about possible problems.
I still can see tons of old style requests for database_api hitting my API endpoints. Guys, seriously?