Before the multiview mode was in krita it was possible to replace an image by drag and drop currently it is only possible to 'insert as new layer',and 'open in a new document' I propose to re-introduce "replace current image" as an option. That option should then just close the image you dropped it on,and open the 2nd image. It's a convenience feature then can help save some time and memory.
I'm pretty sure this is a duplicate, though I can't find it right now. This is quite a bit trickier than it used to be, which is why the feature was dropped. I'm not altogether sure we won't to get into trouble trying to reimplement it :-(
Maybe related to this one: Bug 318560? https://bugs.kde.org/show_bug.cgi?id=318560
I don't think so -- that one is too old, the bug got closed before we merged the multi-document code.
Sorry, we will not in the near future get down to this. WISHGROUP: Out of scope