Scrivening sessions can be used to view items gathered in a collection.
How about the complement of that, i.e. view all items excluding those in specified collections ?
What we plan to do in the future, for both the Mac and Windows version, is increase the utility and power of the project search feature. What you are really describing here is a search function. And it could make sense to have Collections be one type of criteria you could select in a complex search. Being able to tack on “…but NOT in the [Collection Name] collection”, is what I’m thinking of. So I’ve put this on the list for consideration for long-term ideas. Thanks!
Moderator note: I moved this to the Wish List forum.