I just drove a chunk of it a couple of weeks ago in New Mexico. I can' t speak for the other states, but the roads in New Mexico are very smooth and well taken care of....not one pothole or busted up roadway like we have in Calif. It would be a high speed cruisers dream.
Now the bad part is depending on what area you're in, there is Hiway Patrol, Sheriffs, Local cops and Indian reservation law enforcement (or a combination of all of them) more than willing to hand out tickets, and driving everything from sedans to pickups to SUV's.
If I had the chance, I would do it in a heartbeat. Met up with a group of 20 guys from Northern Europe that rented Harleys in LA and are driving the entire length.
Although driving the entire length would be cool, maybe having one group start in Chicago and another group starting from LA ......and meet up somewhere in the middle for a big get together.
Then those that want to continue can road trip back either way, still with a group of Vipers. Might solve the time issue many seem to have.
Make it happen, sounds like fun.
Cheers,
George