Most graduate selection committees will look favorably on a couple of years industrial experience between doing a Masters and doing a PhD. This is irrespective if you continue in physics are switch to a more applied discipline such as engineering. Following the 2008 recession, many people who lost their jobs went back to school to pursue masters and PhD degrees, so this is now quite common.

My opinion is if you are afraid of being locked in, then industry is better place. If you are willing to trade job stability and short term income to not be locked in, then learning how to start and build your own company around your ideas is the best way to retain flexibility.

I did a masters equivalent degree in theoretical physics, now I'm doing a PhD in computer graphics. A coworker who did his PhD in theoretical physics is now doing a post doc in mechatronic. Many people might specialize more and more, but if you don't like that, no one stops you from changing your field.