I think I've seen what you're describing at some outposts like SYR or STL and surprisingly in the old NW A Terminal at DCA.

KLM sometimes does something similar, but they're more likely to just put the blue and white metal sign with the cut-into-the-lane arrow off to the side in the gate area and not even try to follow the system for scanning boarding passes. Once the aircraft actually starts to board (as opposed to the AMS boarding announcement, which really means that one can move into the holding pen at the gate), it's a free-for-all with all rows and all classes rushing at once except for a few who are determined to sit and wait until the last possible minute. (This description applies to flights within Europe. I haven't flown KLM metal long-haul in quite a while, so unfortunately no more Dutch canal houses for me.)