In fact, if I remember well, you sold your first one for a high-res back, didn't work well and then you bought a second one didn't you? ...After all forums are for people learning from one another, I wish more have learned (maybe makers too) from your experience!
Yes, I had a 528c which was great, but I sold it. I wasn't such a fan of the image bank but loved the files. I bought the CF-ii 39MS after the c528. I like it to, but sold it fairly quickly. It wasn't until later that I bought the 80mp back. By that time I had the CF 528 again which is much more convenient than the 528c. It's hard to compare the two - the AFi-ii definitely wins on many counts especially workflow. Multishot does not make good workflow - if you have a lot to shoot the 80mp single shot backs are much more convenient, but I do think the multishot files are very unique - in their own category. You read so much about the Foveon look - punching way over their mp class - well that's nothing new to multishot users.
I never have understood why exactly the multishot had to be exclusively tethered. I mean all those files could be stored to a card in a sequence just the same as single shot files. It would be nice to have that as an option.
Anyhow, I have had a lot of digital backs… I also had a 384c, and a CF-ii 39MS, a p20+, AFi-ii 7. Really all had good qualities. Right now I own the CF 528, and an AFi-ii 12 plus recently I bought a Sinar 54H and have it also fitted to a Rollei 6008AF body and I'm going to compare it to the CF 528.
I do most of my photo work with the AFi-ii 12, but I still like the CF 528 for art reproduction and film 'scanning'. Also its great for table top work with the technical camera since the bigger pixels have less color cast issues than the AFi-ii 12. But for studio work with people the AFi-ii 12 is very nice. Love the revolving sensor - which is simply brilliant.
Back on topic, it sure seems that an adapter based universal back (like the Hasselblad CF line) could be made with multi-shot and for cameras with enough space also with a rotating mount.