A piston system runs cleaner and cooler. There's a good reason that LMG's aren't DI. The only advantage to DI is a slight saving in weight and recoil, IMO.
You still have the same gas coming out the barrels gas port. The heat and dirt just accumulate in a different location. You are cleaning a piston and gas block instead of the BCG.
The 5.56 piston system has the bugs worked out and is a viable option. The 7.62 piston system should be as reliable. Not sure if the extra weight is worth it.
Hanging moving parts on the barrel is counterproductive to accuracy.