Hassy have never used their own sensors, and as they used Kodak made sensors in the past and don't have the size or the budget to make their own, they have to use someone else's sensors, and I guess, right now, Sony was the best they could find.
Canon isn't interested in selling their sensors to anyone else, so Sony was it.
Although I do find it a bit strange that Hassy went to Sony, as they already have an alliance with Fuji, who make the Hassy lenses for their large format cameras (and they are very good too), and Fuji also make reasonable sensors too.
I think it is very brave of Hassy to go into new markets, as in their 70 odd year history, they have only ever made large format cameras, but I guess as this market is now being eaten into so savagely by FF DSLR's as well as the Leaf products and even the Pentax 645, they have to do something to stay bouyant.
They are obviously looking at how Leica can make digital cameras that are well behind the best current technology and still get high prices for them and Hassy are going to do something similar, as they believe they still have a very good name with pros and rich amateurs and offer leading edge tech with cameras made from luxurious materials to appeal those people with money, who want something good, different, luxurious and expensive - but still offering better value for money than Leica.
Personally, I hope they are successful as they are using a slightly different approach to other manufacturers.
Not everyone wants a plain black camera, and I'm sure there are many people who would like to say they have a Hasselblad as it does add some credibility to their photographic prowess, even if they are lousy photographers.