Good to see them asking such questions :-)

I think the current system, if respected and properly implemented, works fine. Having Business and elite(+) passengers starting boarding earlier and at their convenience is a must in my opinion.

I would definitely not implement a boarding by rows from the back, as premium passengers are usually in the front. This results in a lengthy boarding process, long queues, and also problems with overhead luggage bins as people tend to fill sometimes the luggage bins of the front of the plane (not only when the rear is full)