The problem with these proposals is that the passengers' incentives aren't aligned with the airline's. I sit and read a magazine or surf the internet until everyone else has boarded, which minimizes time spent queueing, and that spent in the plane itself. (Of course, this isn't a sustainable strategy for everyone to adopt.)
It depends. If you have a big carry-on, it is in your best interests to get in the plane as quickly as possible, so you don't have to gate-check your bag. This is why first class and elites get to board before everyone else, even if they'd rather be surfing the intarwebs.
