I like the idea but at the same time, I don't think those built in ones are graduated so you can't exactly move them around the horizon line. At first I thought it was a good idea but maybe its best to keep them as screw on or handhelds. IMO opinion, there are not many times that I would like a nongraduated version of an ND to shoot with.
Stuck on what to upgrade to.. EP5 most probable. Wondering if the EP6 will feature PDAF for C-AF and 24p video.. Hmmmm.... relooking at a DP2m as a 2nd body or DP1 for wide angle as I don't think m43s has a good lens below 20mm..