Having just flown on the 4-class 777 (with four club toilets between Club and WT+), the rule is very much ignored, and only some cabin crew make any attempt to stop it. However possibly if you had to walk through the Club Cabin to get to the WCs more of an effort to stop this might be made.

It didn't help that on the aircraft I was on there was no 'Toilets at rear' sign at the front of the WT+ cabin.