I guess over a case a fill is not good enough haha? I'm sure it could be done but the marker runs at 6ms already, how low would you want to go here?
I would be careful with polishing because there is supposed to be certain amounts of friction in the bolt with it's two stages and all, well according to dye. I would mess with orings, less permanent change and it has worked great for me.
I have experimented with running a polished bolt. In my experience it may have decreased the smoothness of the Nt. I brought this up with a Dye tech and was told that the parts inside the firing chamber require some friction in order to function as intended.
Unlike a Shocker or Luxe, the Nt does not suffer from fsdo, thus does not need a spring mod. The Nt is also very efficient so most people do not see additional efficiency as important.