I've used both a traditional putter (Cameron Circa 62) and a version of the long wand known as a "Hammy". I am equally adept at missing four footers with either putter. The Hammy (terrible name, but once used for a season or so by LPGA star Natalie Gulbis) is a longer shafted putter that is used with a split grip and with an very open stance. You almost putt side saddle with this putter. The idea is that you use bicameral vision to gauge distance, break, etc. and then using your bottom hand grip, you 'roll" the club into the ball. Doug Sanders was a pitch man for this putter when it was first marketed as an alternative to traditional putters.
If the putter is held in a split grip but isn't "anchored to the body will it be legal under this new rule? If the USGA and R&A think anchored putters are strange, wait until they see pros putting side saddle - still legal under this proposed new rule if I read it correctly!!
As for any purported advantage with an anchored putter, I would simply point out that you still have to line up a putt calculating speed and break and then hit it.Anchored or not, this is the heart of any putt and no putting technique improves that process..