I'd love the option to hide games I've supported in my library (not delete them, necessarily, just put them somewhere so that they don't show up when I click on the whole collection). Obviously you can carefully curate your individual purchases, but buying bundles means you frequently get a lot of games you don't actually intend on playing, which make it harder to browse your collection for games to download. Steam has this feature, and I've also found it useful for hiding games I've already played and not enjoyed.

You can just create a whole new collection for "things I actually want to play" currently, but then you have the extra work of adding your new purchases to that collection each time instead of it being done automatically for you.

Just found this thread while searching how to do exactly this.  I bought the GDC bundle to help out people, but I intend to play maybe 2-3 games out of the 100+ plus that are now crowding my library.  I'd love to just tag the ones I want into a collection and mass dump the rest into a bucket that pretends they don't exist unless I specifically look in there.  Currently when I go into my library page all the stuff I don't want to see is listed at the very top of the page under Things I Own.  I don't have a whole lot of games here, so I haven't needed collections to keep things organized.  Literally everything I had was easily visible where I wanted to see it.  Now it's not.