Piston Rifles are not new. They have been around for years. The only problem I have with buying piston in an AR15 is that the systems are proprietary. If something breaks in the piston system you are going to be down till you get the part in. Plus there is no clear cut advantage for it over owning a DI AR15. You can build an AR10 in 7.62 but the ammo costs are higher.
Have a nice day at the range
NRA Life Member