I would have no problem with that, I generally do 80-90 anyway when conditions allow.
Maybe they should just "decriminalise" it if you will, so if conditions are good and traffic is flowing nicely you can cruise along at a decent pace, but if you are spotted driving innapropriatley, then you would be in trouble.
The biggest issue on Mways is lane discipline (not moving left when people probably should), and general awareness and lack of progressive driving- thats what causes most hold ups, the need for heavy braking and, I dare say most accidents...
If you are looking ahead and undersanding whats happening and identifying what manovers the trafic ahead are likely to want to do, its very rare you even need to brake, you can just ease off a bit. The more congested it is, the harder it is to make these predictions.
That though, is very hard to control, its much easier to control speed en masse, but as im sure most will agree, speed in itself is not the main issue, its driver behaviour.