i think it would be a huge mistake for the U.S. to move in the direction of more specialization rather than less. controlling for all other factors, our obsession with specializing is one of the major reasons why our health care costs are so much higher than other industrialized nations. i also think it's vital for patients with multiple medical conditions to have someone coordinating all this care. if they only go to see independent specialists who have minimal communication with each other, quality of care will really suffer.
i have to agree with some of the remarks above, i think primary care doctors are going to have a more managerial/support role in their practices. they won't see routine patients, or do as much preventive care, that will be handled by midlevel providers. what they will do is see more complicated/chronic cases. the drawback is that there won't be as much of the traditional, continuity-of-care going on. as a PCP, the first time you'll see a patient will be when they're very sick. no more following the same patients through both sickness and health, so that you know them as a "whole person"
in any case, i think that if you are very serious about being a rural doc in a small town, you should think about how you'll best serve the community. it may be that you'd be of most use if you got training in family medicine: that way, you'd have the ability to take care of whatever walks in your door, including children and pregnant women, and you'd have more training to do minor procedures and take care of musculoskeletal problems. my impression is that IM residencies are mainly focused on inpatient care, and that's not even what you want to do, right? also, keep in mind that increasingly, internists are getting pigeonhold into seeing mainly geriatric patients. if you love that patient population, great. if you want more variety, family practice may give you more opportunities. there's an interesting post in the FP forum right now by someone who regrets going into IM instead of FP.
finally, while i appreciate that you find the intellectual challenges of IM more intriguing than those of FP, keep in mind that once you're out in the real world practicing, there's not going to be a whole lot of difference in your day-to-day life, and how much intellectual challenge you get. a primary care doctor is a primary care doctor, the major difference is in who you're qualified to see.