I'm not familiar with the phrase, "darkslide curtain". I am quite familiar with med format cameras in general and darkslides though...I know the Hassy H1 or Hseries has a built in darkslide. Maybe that could be referred to as a "dark slide curtain".
Or, upon re-reading your entry I figure this is something just for the changing of lenses. I guess that is a significant improvement if you used to have to unmount the camera from a tripod but the others seem not such a big deal.
I want to get a medium format film camera and the Fuji GS645 and Mamiya 7II are both on my list... the Fuji I really want for it's synching capabilities and the Mamiya of course for its big neg and varifocal attributes. I've seen a beater Mamiya 7 on here for $470 and a Fuji on eBay for $500 with new bellows... can't do anything until next week so it may be a mute point, but if anyone wants to chime in on the value of these cameras I am all ears... or uh, eyes.