Ironically, this all seems to come back to a little common sense on the part of travellers and gate agents and some general decency.

For the most part people have said:

Those with special needs should clearly be allowed to board early, especially as it makes it easier for everyone else to board (imagine a 2 year-old holding up an entire plan as they want to crawl all over J-class seats etc.). However, these priveleges are not to be abused -- e.g., one couple or passenger should be allowed to board with a child, not an entire group of adults.

Full fare J, SE, E priveleges should be respected both by those who earn them (e.g., don't be a jack-...), those who don't have them, and most importantly the gate agents / AC

Boarding calls / process should be stated clearly and enforced to avoid confusion, in addition the process should be consistent on all AC flights

Economy class passengers, lacking status should be made aware of these procedures and kindly informed that Air Canada grants special priveleges to those who remain loyal to the airline. One of these priveleges is to board the plane early and get settled into their seats without having to deal with a massive throng of people boarding a plane.

My general rule of thumb is treat everyone else with respect and decency, even if they are being ridiculous. Seems to work fairly well.