I'm sure I'll not be the first person to do this.* I think it would be ideal if XNView prompts to confirm when dragging in a large number of files. I would suggest a prompt for 10+ files (if there is an existing setting then it must be too high!) I'm not sure if the escape has been implemented, but if not hitting the escape should pause any opening and ask whether to continue or abort, so someone dragging in say 9 files (below the prompt) can still abort the action.
David