1) You're not going to get a definitive answer on the future of any medical specialty or medical reimbursement structure. It's speculative. The practice rights of NPs might get beaten back, stay static, or expand. It would need to expand REALLY fast to eat the market for FPs, because our population is getting drastically older and sicker.
2) You might not be interested in Primary care once you finish your training. There's a reason so many people run to tertiary care: primary care is fairly forumlaic and what seems interesting when you first learn it can seem very repetitive. An MD has more options if you end up hating clinic.
3) You also don't know what's going to happen with the market in technology. In a decade primary care might be driven by techs with Watson style programs. An MD gives you a wider range of options if you need to retrain.
4) I wouldn't want to practice 3 years after graduating college and you shouldn't either. The NP degree was designed with the idea that experienced nurses would use the knowledge base they developed working on floors, in ERs, and in ICUs to replace the time they wouldn't spend training in medical school and residency. That premise alone is questionable, but these 3 year straight to NP programs (yes they do exist) are disgraceful. I've worked with one graduate from such a program an she functioned at about the level of a 3rd year medical student, which is not surprising since she had 3 years of training. I'm surprised nurses don't rise up against these programs for f-ing up their brand: just like you shouldn't be able to call yourself a doctor without being one you shouldn't be able to call yourself a nuse if you've never done and never plan to do any nursing.
I hate to be the melodramatic guy but this is a life and death profession. I've just finished four years of medical school and I'm horrified that they're going to trust me to be a very closely supervised Intern. If you think you're going to be ready to practice independently in less time than it took me just to feel this unprepared for an Internship I think you either need less confidence or more concern for your patients. If you want to be an NP I strongly believe you should plan to spend at least a couple of years nursing, ideally in a 'learning heavy' enviornment like the ER or an ICU.
Summary: I would be an MD. If only because you might end up really like surgery/gas/medical subspecialties. Failing that I would be a real nurse for awhile before becoming an NP.
There is no course quite as useless for your future medical career as organic chemistry. Good for them.