KISS principle. Just improve the existing shoulders (many are already simply beautiful) and let us use the darn things. Yeah, bike-cage accidents would probably be fatal for the cyclist, but I rode portions I-25 in NM and Colorado for 10 years and never even had a close call. The biggest danger isn't pissed off people trying to run you down, because you are not blocking their path or causing them to have to change lanes to pass you. Jerks who use the shoulder as a lane to bypass traffic are a danger, as is debris, both on the shoulder and flying up from truck wash, which is another danger...darn trucks can blow you clear to Kansas. Motorists who need to pull to the shoulder for emergencies are a risk, especially at night when tired drivers get to wandering. No problems with trying to merge into traffic lanes to take a left, we follow the same traffic patterns using off-ramps, which are also usually well shouldered. No parked cars to worry about, very few peds, not a lot of loose dogs, at least not live ones.

My experience in NM may not be a good indicator...traffic volume on 25 at the NM-CO border isn't that heavy, and I have not thought this totally through...but that's why I mentioned it...lotta smart, experienced cyclists around here make for a hell of a brainstorming group.