What is this guy's interest in the M20 and why does he want his private license so quickly? Aside from the training you referred to, this guy should make sure the M20 actually fits the mission for whatever flying he plans to do after getting his license. A lot of people get infatuated by top speed specs and would ultimately be happier in a plane that is 20 knots slower if it can carry more, have simpler maintenance, and be easier for a low time pilot to fly.
I don't know much about the M20 series, but I don't see anything inherently wrong with training a low time (or zero time) pilot to fly high performance aircraft. I'm currently working with several clients doing similar training. A student pilot in a 182, a low time private pilot working on his instrument rating in a turbo 206, and still another in an SR-22, and it's working fine.
That said, be aware of a few caveats. It will take longer to become proficient, so don't try to rush. What might take 40 hours to learn in a 172 might take 40 hours in an M20, or it might take twice or three times as long. Who knows. Both client and instructor have to be patient and not compare apples to oranges.
As an instructor, make sure you're very comfortable with the limits of the plane before trying to teach it to somebody else. Mooneys don't land like Cessnas, so you'll have to be on your toes, especially during the initial stages of teaching him how to land. You probably shouldn't let botched landings go as far as you might in a plane built to be a trainer.
As far as complex training goes, teach it like anything else. Just do it. It's another thing to learn, which is why I say it might take extra time for him to become proficient, but that's life. Just like how we teach people about flaps and carb heat in the pattern, your guy will also need to learn to handle the prop and gear.
If the guy understands these factors and still wants to buy/train in the plane, go for it. It's not the easiest or cheapest way to get the job done, but I don't see any reason why it's impossible.
