If you want to pursue both fields, you would probably have to own your own business and create the model for it. Hospitals and established clinics are not going to hire someone to do both positions, even if they are in need of both a PT and RD. It just isn't realistic. It's likely that if you become an RD and then go to PT school, you will end up working as a PT and the RD will be a nice side note on your resume. That being said, with the expanding wellness market, a combo PT/RD could be useful. Though you would have to offer the two services at distinctly different times if you are looking for insurance to reimburse you. There's no way that you could do a 90 minute PT & nutrition eval appointment unless your patients/clients pay out of pocket.
I don't see why you should be worried about keeping up with continuing ed. The hardest part would be getting your employer to pay for CME for both professions. If they hired a PT, they probably aren't going to pay for you to attend a dietetics conference.
Unless you have a strong passion and clear idea of how you will combine PT and RD, I would pick one and stick with it.