In order for the concept to work, it has to be bikes only, enforced and limited access... just like a motor vehicle limited access freeway. It may be at ground level, but it cannot be like most "paths" that badly meet regular streets.
The whole concept is based on making cycle transportation faster and more efficient... just like an interstate hiway system.
Consider just for a moment that as cyclists we are stuck on surface streets and therefore are subject to lots of stop and go... which we really hate as it kills momentum. If a limited access freeway-like "bikeway" was built to allow for fast cross town trips, think about how this could decrease the time it would take for a cyclist to move across town, unencumbered by intersections and traffic lights... it might be quite an encouragement for folks who now believe that certain trips just take too long on a bike.
The lack of intersections with autos could also be a huge safety factor. I for one would love to dash across town at my highest speed possible, rather then moderating my speed for traffic, and killing my momentum for lights and signs.