one alternative to both climbers seconding at once, is that climber B seconds fast and leaves the gear in, and climber 3 follows on a Ushba Basic on a fixed rope, and takes the gear out.
We did this on a summer climb of Rock On, left the car at 9:00 PM and topped out at 11:30 PM i havent done it much in the alpine, and it isnt the greatest method for fullpitch traverses - or when the leader needs the gear back for the next lead. but if you take a rack and a half it works fine.
one thing i have found about reversos for 2 or 3, is that you really have to be a few feet below the anchor for them to work in the autolock mode. so if your clip in to the anchor on an alpine route is to gear at waist level, and you cant get below it to pull on the ropes, youre gonna be screwed. also they are suck when the route is low angle.