P: Show collection list in folder list

this shows only the list, bu doesn't allow to add images to already used collections. Again: "The intention behind this idea is solely to simplify the sorting of images into collections which are already used in the folder."

@hermann.weiss.vista said: "Showing the used collections "inside" the folder structure is only one option. They can be displayed also on the top of the grid view, perhaps as an icon and hovering over it with the mouse the collections list appears"

I'm not sure how different this is than using the context menu?   Ctrl/Cmd+a to select all images in folder, then right click on any of them and pick "go to collection".  Maybe an extra click or two but it does give you your list of all candidate collections which I think was your goal.   

However this is probably a moot discussion as Adobe is unlikely to see this topic as worthy of investment so at this point it is really just an academic debate.

You then get a list of all the Collections pertaining to all the selected images.

yes, the list can be quite long in exceptional cases, but what does it matter? Especially when sorting the images, it would be useful to have all the collections that have been used so far in front of you. Smart Collections should not even be displayed here.

Regarding the parent folder: no, only the collections of the selected folder should be displayed.

Showing the used collections "inside" the folder structure is only one option. They can be displayed also on the top of the grid view, perhaps as an icon and hovering over it with the mouse the collections list appears... drag an drop of images must be possible.

The intention behind this idea is solely to simplify the sorting of images into collections which are already used in the folder.

any individual image can be in a dozen or more collections.  And a folder full of images can relate to many dozens of collections.  here's a screen shot of the colections related to just one of my folders

How do you propose this work?   If you are looking at a folder are you suggesting that every collection containing ANY image in that folder in be listed?    

What about a parent folder when you have "show images in subfolders" is turned on?  Do you want every collection represented by all the images in that parent folder along with all it's subfolders to appear under the parent folder?

Usually most folders in the folder tree are collapsed. If the collections are only shown for the selected folder (or even all expanded folders) this should be no problem, e. g. 3 used collections in a folder shows only 3 collections.

I don't think this is practical as a collection more often than not contains images from multiple folders.  If Ihave a collection of "Favorite" images that contain images from dozens if not hundreds of folders, where would that colection go in your proposal?  Would the "Favorites" collection be listed under each and every folder from which it has one or more images?  That could be a VERY long list.