There are all kinds of threads here on different MF digital subjects, cameras, backs, software and adaptability. I thought it might be useful to start a thread to discuss all this in one place as a central resource.
First, I'd state an opinion: Nothing in the 35 DSLR world even approaches the IQ abilities of these MF backs. I do not think that will change unless there is some incredible technological breakthrough in imaging ... and one would presuppose that breakthrough could also be applied to MF ... it seems "size will always matter" just as it did with film.
WHAT CAMERA/BACK SYSTEM?
I think one of the most important subjects being discussed is digital back platform compatibility. Broadly speaking, there seems to be two digital camps: "Cross Platform" (probably best personified by Sinar), and "Dedicated" (probably best personified by Hasselblad H3/3-II.)
I freely admit that this subject is confusing to me. For example, to this day Hasselblad still offers CF and CF/MS digital backs that use iAdapters (many with direct electronic data bus connections) to fit the Contax 645, Rollei 6000 series, Mamiya 645AFD & Pro, Mamiya RZ & RB, Fuji GX680 ... plus every Hasselblad camera ever made including the 200 series using C type lenses (Sinar is the only one that supports the 200 series with FE optics).
CAMERAS: I've owned and used everything MF out there except an ALPA & Hy6 (which I've used briefly). To my way of thinking there are just two broad categories of MF cameras: "Leaf Shutter", and "Focal Plane Shutter". In more recent years AF was added as a feature in both "shutter type" categories ... Contax 645, Mamiya AFD (& recently Mamiya/PhaseOne) ... AND Hasselblad H, Rollei AF leading to the Hy6. Older "legacy" manual focus systems like the Hasselblad V, Rollei manual, Mamiya RZ Pro-II and even Bronica are still out there trucking along with digital backs. I'm not differentiating here based on 645 verses 6X6 or 6X7 because there are no digital sensors larger than 645 and speculating on that future possibility just confuses the current decision issues even more. Currently 645 is where it's at because the wide angle lenses are wide angle.
Now, here's another point of confusion: Digital backs with dedicated mounts like Phase One, Leaf Aptus, and older Hasselbald/Imacon could be configured with the so called "Universal V" mount ... which, with the use of adapters, could be used on a number of platforms: Hasselblad 500 series, Mamiya RZ, Fuji, Bronica, ALPA, and virtually every view camera made. Not quite the versatility of Sinar or Hasselblad CF backs which seem to adapt to even more platforms, but pretty good coverage.
I think the versatility issue revolves around the desire to use one of these VERY expensive digital backs with both MF shutter systems ... like on a Contax 645 and a Mamiya RZ or Hassey 503CW. Contax was suppose to come out with come leaf shutter lenses (never did) and the new PhaseOne/Mamiya AFD are also suppose to.
THE ROLE OPTICS PLAY IN THE DECISION PROCESS:
Many of us are influenced by optical choices and have a bias. That argument is one that can't be won. Besides, on most of these MF cameras you can adapt different lenses systems, so it's often a mute argument.
In fact, I considered Hasselbald H only after they offered the CF adapter which allowed use of my entire CFi, and CFE lens line-up with full aperture metering and focusing ... while taking advantage of the in-viewfinder focus confirmation.
Another mute point IMO. If the software isn't what is needed to be competitive it soon will be. C1 is excellent, Phocus promises to also be excellent, Sinar is here with new processing software, Leaf has always been supported by Adobe as is the ZD. By mid year all this will be sorted out, and I doubt software will be a deciding point any longer.
you really can't go wrong with any approach. If you want to continue using 5 different MF camera systems there are excellent choices. If you want a dedicated and integrated system, there are equally excellent choices.
Personally, I wasn't interested in versatility despite owing 2 Hasselblad V systems (500 & 200), a Contax 645, and a complete RZ Pro-II system ... then a Mamiya AFD-II with a Leaf back ... it was getting ridiculously expensive to maintain it all ... plus, I have to have 2 digital backs no matter what. Clinging to past legacy systems or dead-end ones seemed to be a path to ruin. So, I decided on the H system and using them with H/C AF lenses as well as all ready paid for CFi & CFE optics. I prefer the whole H handling experience and integrated approach which I've now used under fire, on the job, job after job.
Swapping systems has gotten outrageously, mind numbingly expensive, and from a business POV is not justifiable. I will not do it again. If I want to use my old legacy cameras I may get a used Sinar ... but frankly, it's an idiosyncratic extravagance that in the real world is neither needed nor justifiable. My best move would be to just sell it all off except the CFi and CFE lenses. Watch the F/S forum, it may soon "Fatten Up" with some pretty good MF deals : -)