Emil
I took a look at your work.... nice. You are certainly achieving well with the Canon.
Regarding MFD as an upgrade from that you have I would not bother with anything with a sensor that is 33x44mm... it's just too close to 24x36 especially if you consider that the newest 35mm FF sensors are more advanced.
More than the type of work you do determining if upgrading to MFD is worth while you should decide more based on how your work is published.
This comparison should help. Keep in mind it is a comparison between the D800 and the very top of the line MFB the IQ180.
http://www.circleofconfusion.ie/d800e-vs-phase-one-iq180/What I am getting at is that if your work is not printed very large AND VIEWED CLOSE the difference in quality is not that significant.
I think it is important to keep in mind that today quality levels are so high that the quality from less expensive cameras is more than sufficient for the vast majority of publications or use by commercial customers.
With quality levels this high over the board it is becoming more about content and the quality you produce in front of the lens.
Anyway I think that your idea of getting the Hassy 39 is a good idea to "investigate" MFD and see how you like it.
It's not too expensive and at a price that enthusiasts would still buy one for so if you decide to go in another direction
you can re sell it at about the same price +/-.
As far as getting an IQ back instead of the Hasselblad keep in mind that the technology difference from an image quality point of view is not that significant. It's more about ergonomics and screen. There are some improvements like better live view, but that live view is still far inferior to what you have with Canon. Also an 80MP sensor is not twice as sharp as a 40MP sensor. Sharpness is a linear function so look at horizontal pixel count. 7212 vs 10328.
One last thing. Before getting an MFD system I would take a close look at Carl Zeiss's new lenses for 35mm cameras. Very large lens designs that might just be what the top FF 35mm dslr cameras may need to show their full potential. The over size designs give the designer more freedom to produce a different type of look.