When opening the dialog "Batch convert...", I guess (novice) users are a bit baffled since there are many options.
Dialog "Batch Convert" in XnView 1.80:
A new, clearer layout would make things clearer and even easier to handle:
Suggestion A:
The charme of solution A.) is that the "Advanced operations" (here: "Transformations") are not a sub dialog which is opened by button "Advanced" but a simple folder tab.
Suggestion B:
When applying the tab approach consequently, output and input may become own folder tabs, which would like this:

On the tab "Output", the file list is shown but only read-only.
The tab "Input" would also have the file list with buttons to add files and folders and remove them. (For slide show there would be also a preview and the "Sort" buttons).
To make this solution B.) work well, XnView would switch to the "Input" page in case the list of files is empty. If it's not empty, the "Output" tab will be opened automatically.
The good thing of this solution is its simpliness (the tab page "Output" looks almost as simple as the "Save" dialog). And this approach could be applied for the slide show and other multi operations. See also discussion in topic
"Unified way for creating file list".
I expect some people complaining and not wanting a folder tab approach. Please have a look at the above approach and really try to "feel" how it works. Let's then discuss this and see.
Comments are welcome...