I would like to respond from an user's perspective. In one of my assignments I used automatic broadcasting and provided the code to my professor for grading. So far I was assuming that Matlab supports automatic broadcasting. Luckily my professor used Octave to evaluate which may not be the case always. After seeing this discussion I could understand that Matlab does not support this. As an user I don't know which feature is available in or not available in Matlab.
It will be better to show matlab incompatibility warning than the current warning.