Even though this is a (proposed) stroke ban and not an equipment ban, I think this would basically ban the belly putter. I dont see how they can be used un-anchored. (probably because I never tried one)
Belly putter use may be more prevalent than any of us realize because it may not be obvious that a golfer is carrying one. Broomstick putters stick out, the belly putters do not unless you are watching someone on the green while you play.
I forget the post, but earlier someone stated that this whole *comment period* was nothing more than the USGA + R+A coming up with ways to fight any proposed arguments against the (proposed) ban and word the ruling to protect themselves against any frivolous lawsuits.
Matt Kuchar uses a belly putter unanchored. Odyssey has said that they will be offering a couple of putters designed with the loft designed for this stroke.