The kids are getting older and I have a 3rd one now (she's 7 months old).
Remember that you can't practice medicine after graduating from med school. You need to complete a residency as well.
Your view on medicine is appreciated, but it's quite simplistic. An internist or FP often doesn't confirm diagnosis of all those items you mentioned, so it would be unrealistic for a dentist (with the hypothetical MD) to do so. They often make the initial diagnosis but don't provide comprehensive treatment. A generalist often sends the patient to an endocrinologist, cardiologist, etc. for confirmation and management of those conditions.
Further, nobody will go to a dentist for treatment of those conditions, regardless of your degrees, unless you are solely practicing medicine. Your idea is a fun one to toy with for some, but in reality results in a dentist that practices crappy dentistry and half-baked medicine. A jack of all trades is a master of none.