Another simple solution would be to board from back-to-front. Right now it's front-to-back: the business-class passengers (at the front of the plane) board first. Economy class boards last and each passenger has to walk through the congestion.
Getting business-class travellers to give up their sense of entitlement and board last could be a little tricky, though. I'm sure there's a psychological marketing trick that could be used to make them happy about boarding last. Maybe something along the lines of, "You're special. Boarding starts 10 minutes later for business-class. Take your time" or something.
I always board last. I'm going to be spending too many hours on the plane anyway, why would I want to spend yet another hour sitting motionless on the tarmac when I could be out where there's power and wifi and restrooms? So I book an aisle seat and ignore the zone calls and get in line near the very end.
Then I make up for being in some way possibly antisocial by helping someone with their luggage or something.
(As noted, I don't pay too much attention to it, but I do think they often board the tailies before the center on at least some airlines.)
Virgin America seems to board back to front (after first class, families, etc.) and it tends to be just as time consuming as boarding front to back in my experience. It's even worse because the people sitting back occasionally decide to put their bags in the front above seats that haven't even started boarding that need their own bag space in return. I think boarding any which way with one piece of small carryon or similar will do far more than the order in which you have people board.
Most airlines board back to front, excluding business and first of course. But it just ends up taking the same amount of time as front to back. It's not the people taking seats on an empty plane that is the problem. It's the last few that are having trouble finding overhead storage and have to hunt up and down the aisle for a place to put their bag.
Also, you can't give up business entitlement. It's built into the price and the passengers paid for it. The entire reason they buy F/J tickets are boarding priority, good seats, better food, newer IFEs, and higher luggage allowances. They also get a glass of champagne or wine, something they wouldn't be able to receive if they were the last to board.
Also a coach and F/J fare is the difference between a $1/pass and $1000/pass profit.
When I've flown first, I can say that I would rather spend those 10 minutes being pampered ("would you like a drink?") than waiting in the general lounge.
Now, if I could be in the club lounge, that's a different thing. Being bumped to first class doesn't get you that level of access.
Getting business-class travellers to give up their sense of entitlement and board last could be a little tricky, though. I'm sure there's a psychological marketing trick that could be used to make them happy about boarding last. Maybe something along the lines of, "You're special. Boarding starts 10 minutes later for business-class. Take your time" or something.