this was (and could be in the future) a really cool feature.
(yes, i know there is the preview-feature (with bugs); no, i do not want to use gnome-sushi with nautilus (even i know some guys who only use it because of the sushi-feature). no, i did not say it would be the next cube-effect)
klook is already there. it is simply very useful and could save users lots of opening and closing-clicks (or fiddeling around with preview).
I’m not following this space in general, the only thing I’ll point out is that an incubation request showed up on a KDE mailing list recently: Incubation Request: Kiview
According to some reviews on the thread, there are still some technical issues with this new quick-look app. I don’t know why they would choose to go for a new app as opposed to resurrecting Klook, but every developer has their own goals and makes their own judgment calls.
Fun fact: I got interviewed by the original developer of Klook a while back, he’s really nice and knowledgeable. (Unfortunately, the company decided to ghost me when they decided not to go forward with the application. Oh well.)