Having worked as cabin crew on everything from props to jumbos I've seen and tried various slides. The bigger the slide the quicker the evacuation seems to be. One thing we were always taught was to keep the flow of passengers going even on a single person slide. This is not as easy as it sounds. You naturally stop at the top of the slide to allow more space between yourself and the person before you. You also are relying on the ABP's at the bottom to do their job and move people away to prevent a human pile up. What would make more sense would be slides that expand sideways as well as move out from the fuselage. By being slightly wider you could put a divide down the middle and create two lanes. This would give you a greater capacity but without having to make slides the size of some of those on the jumbo. Even with a normal size single door you could then evacuate quicker using the sides alternately. On the smaller single aisle aircraft, the 250 pax or less variety, space is tight, especially in an evacuation. If you can get them moving quicker I think there's more hope. The only technical problems I can see are that a) the floor fittings for this slightly larger, heavier slide would have to be beefed up a bit b) the bussle on the door would be a bit bigger and c) the increased weight will mean more fuel burnt. A reduction in the size of bars carried and number of glass over plastic bottles carried would help to offset this!
Best Regards