A Whole Foods in NY has that. Everyone just gets into 3 lines and a note pops up telling you which cashier to go to. I think they have 3 lanes just to hold more people - the system would be identical with any N lanes.
I sometimes wonder if people at the Whole Foods think they have to use the express if they have fewer than 10 items.
The trick to this is to gather all the items not bordering the line, then get in line and shop while you advance in line.