They are totally different media. Scanning black and white film does not usually show it to its best advantage, but there are some good reasons that one might choose to do so. 1. Different films have distinct looks -- their characteristic curve (their tonality and response to different light levels), grain and so on. If you find a film/developer combo you like, it is like a preset.
2. Film and digital have fundamentally different behaviors in reaction to light -- neither is necessarily better or worse, but they are certainly different. Pick the one you like better.
3. The Hy6 is a 6x6 camera, and the 6x6 film back allows you to use the camera as it was designed -- the full viewfinder, full lens circle, no masks, no rotating etc. If you like using square compositions, it is 56x56mm instead of 36x36mm.
4. A film back is a nice backup even if you use primarily digital. You can use it in situations where Sinar digital backs do not work (exposures over 32 seconds, high ISO's up to 6400 or so (delta 3200, provia 400x etc), or when you just want a different look).
5. I am sure there are other reasons too, but I need to go to work. Suffice to say, for a lot of people it is a really nice addition. I was begging for it for a year ago, but they never confirmed to me that they would actually make it and then they went out of business (or so they said), which is what eventually caused me to sell the camera. Now I use the 6008AF, almost exclusively with the 6x6 back.
As for the price -- I am sure it will be extremely expensive -- 1000 USD or so would be my guess. I do think it will be cheaper to buy a used 6008 camera, but then you don't get the nice advantages of the Hy6...the ergonomics, shutter damping, battery life etc etc.