The key to all this is that, given good information, most (although not all) drivers will cooperate. It is the apparent irrelevance of the limits that causes people to get hot under the collar, probably exacerbated by the fact that they have no trust in the general motorway signalling system that operators "forget" to cancel restrictions on, long after the need for the restriction has gone.
I remember driving on the Paris Peripherique many years ago and thinking what an excellent idea the real-time signage was that told you how long it would take to get to each of the next few exits. Instead of sitting in a queue of stationary traffic wondering if it extended for the next 400m or 4km, and not knowing whether you were going to take minutes or hours to get to your exit, you knew. Perhaps there should be similar real-time information posted on "Smart" motorways when speed limits are set lower than the default 70mph?