I have been the "expert" in many situations, and no way would I let this happen.
1.) Mentoring is such a difficult aspect as an expert. I likely would have built up my expertise from a combination of my studies, my past work experience and my previous, extremely skilled mentors. I can't expect people to get up to speed simply through my mentoring alone - especially if I'm not a capable enough communicator.
2.) Experts like to retain their expertise, stay unique. Regardless of what idealistic scenario you have in mind, everywhere I've seen, experts are always very cautious to giving away ground. I've been guilty of it, especially when I knew that my unique expertise was responsible for my sizeable bonus check in an IB.
3.) Experts will not do all the grunt work you mentioned. They come with the expectation that they've been hired for their expertise and not to be another cog in the wheel, but the engine itself (for a particular project).
Ideally now, what you would want would be a team of generalists, and a small crack team of experts (or a lone wolf expert). The generalists set up the project, plan how to build the guard rails, etc, then explain it to the experts, then when both are up to speed, generalists build it out and give the heavy lifting work to the experts to take over from.
Converting a generalist to an expert is a time intensive process that has to be structured and well-thought out. It should not be for just one project, but should continue for multiple projects.