The advantage of MFD is a bigger sensor, as compared to a D800. The croped sensors of the HXD-31 and 40, the Pentax 645D, Phase P30, Leaf Aptus 6, aren't that much bigger than 35mm FF.
If I had $14k burning a hole in my pocket, and I needed a 30mm field of view on an MFD set up, I wouldn't get an H. The wide lenses are very expensive, like an additional $2k used. I would probably go for a Leaf Aptus 75s (Aptus II 7) and an RZ67 with the 50 ULD lens, and a Mamiya AFdII - Phase 645DF with 45mm. The whole set up used could be had for $8k used. The RZ is a pain to lug around and doesn't like water, ut the lenses are amazing and you can have tilt shift. The mamiya AFd/Phase cameras are less than ideal, but I really like the lenses.
Frankly, I think a D800e and some choice lenses would be the ideal solution. While I think the new MFD full frame backs have some advantages over the D800e, the difference in image quality is at the margins. The major difference is the camera and whether you enjoy working with MF. Its a mixed bag.