We are entering a period where medium format companies are producing and considering the entire product (digital back, camera, lens, etc) to be their proprietary intellectual property.
To be sure, Jenoptik desired the Hy6 camera to be on more than the Sinar platform, since - to this point - Sinar has trailed in market share compared to Leaf, Phase, Hasselblad. So, they made an agreement with Leaf and that fulfilled the number of units they were looking for to make the project a financial success. It's possible there was negotiation or bidding with Phase, and Leaf simply won that process - made a larger financial committment, etc.
Leaf also has much more symbiotic history with Sinar than Phase One does. And that could have been a factor. But we don't know exactly what happened.
I don't know why any digital back manufacturer couldn't fashion a mounting plate and - using a flash sync cable - make a digital back work on a Hy6. But there may be more to it than this, and it's possible that if Jenoptik truly want to keep this between Leaf and Sinar - hey Phase, go make your own camera! - then you could imagine a created firmware in the future that changes internal timings, etc that make even a flash sync communication difficult. That would be pretty hard core though.
But the intellectual property aspect of this could very well play a role, and a manufacturer who creates a complete medium format digital solution may have the right, and the ability to invoke such a privilege. Is it right for the photographic community or Phase One users in particular? Not necessarily, but we're entering an era of complete systems, and I believe this will propel Phase One to get into the game, which they're long overdue at joining. That certainly would be positive for Phase One users. In the past, the choices have been which digital back do I put on my film camera? In the present and future, the choices will be which digital camera system do I go with?
Steve Hendrix
www.ppratlanta.com/digital.php