This is an extremely bad idea for several reasons.
First, if you have a DPC you're expecting patients to pay cash. You have to offer quality in exchange for that. A decent subset of your patients will care that you both didn't finish residency and aren't board certified. When I had my DPC practice somewhere around 50% of patients asked if I was board certified. Now if you're the only DPC in your area and don't care if you only get the patients who have no where else to go (uninsured, hate the other groups in town, super libertarian) this might not matter as much but that's a risk.
Second, in DPC you actually need to be better trained than the average FP since many of your patients won't be able to access specialists. Where I was, the only rheumatology practice would not see self-pay patients whatsoever which means I had to manage these patients' RA, lupus, psoriatic arthritis, you get the idea. Being able to look things up certainly helped, but you need a certain amount of previous knowledge and experience for it to be even reasonably safe. Same thing with ortho stuff. I had quite a few patients needing injections for things I hadn't trained to do but because I had done lots of injections in other areas the skills transferred well. Its like how surgeons don't have to go back to residency to learn every new procedure that comes out because they have a solid foundation of knowledge/skills.
Third, FM residency is somewhat unique in that we have significantly more elective time in the later years than most - its why there is such a wide range of practices in the field. You're really screwing yourself if you throw away the only chance you'll have to learn directly from the various specialists your program will have you rotate with. If you're driven, you can even learn more unique skills that can really help a DPC practice - vasectomy, ultrasound, splinting/casting, more advanced GYN procedures (endometrial biopsies, IUD placement), stuff like that.
Fourth, if your DPC practice doesn't work out for any reason if you aren't residency-trained and board certified finding another job is much more difficult. Not impossible, but your options will be severely limited.