Thanks for your feedback! I was thinking about this in a different direction, coming from the application and with the strong impression it would be extremely useful. This leads to a different model:
With that feature in place, collections would be on top of the filters, meaning that you would be able to view only one collection within the collection paradigm. Something like an additional module/entry/whatever “above” the filters of the collect module to select a collection to view and having only one such an entry. Default is no collection selected. The filters of the collect module would default to AND with the named collection, but OR could be selected to allow to show additional images, maybe for adding to that collection. With OR activated, the collection would no longer be sorted but the default sorting would apply, with the collection’s images having another frame colour to highlight that they are part of the selected collection. With a collection selected, you would have two additional sorting options “collection order” and “reverse collection order”. If a collection is created out of a set of images, the default order would be by date, if pictures are added to an existing collection, a dialog would ask if it should be placed at the beginning or end or between the closest subsequent date pair of the collection (or only the first two options).
I would either not allow dragging images when not in a collection view, or, have a second paradigm for that, ordered grouping. The latter is not thought about carefully enough (at least not by me), so I would start with the first one.
This is of course not an option. I hope my description how things could work together above makes sense .