I’ve been thinking about this and although I’m not a developer, let alone a GUI designer, I would like to offer you the following to consider.
RFD supports having multiple configurations so the most logical place to implement this would be the Photo Subfolder Generation Editor which is where these configurations are made. A new section, below Job code seems appropriate.
English isn’t my first language so take the suggested name with a grain of salt, but Inclusions sounds at least halfway right. It should signify that what is going to be copied.
Although the original request was to be able to exclude things I think that including will be a better starting point then excluding. RFD is about copying files from A to B, having a way to select what to copy makes more sense to me then an option that wants to know what not to copy.
The current way the sections in the generation editor are set up seem very straight forward and I think this structure can/should also be used for this added functionality (a pull-down list of options). There’s already a predetermined list of extensions/formats present, which can be used.
Out of the box this option should be set to All, which is the current and sensible default.
At the top, separated by a line, add some grouped options (e.g.: All/RAWs only/ All audio/video/non-RAWs/…/…). Do make it so that only a single entry can be selected from this list.
Unlike the other options in this menu there will not be an Insert button. The inclusion that is chosen will be shown (same as the other options).
There is one thing that the above does not do: Multiple, individual extension (e.g.: only NEFs and JPGs). I personally think that this would be out-of-scope for what RFD is supposed to do and groups can handle all the logical/common scenarios. If I look at fileformats.py these groups are all but defined already to begin with.
I do realize that this setup does not give one the option to exclude one specific format, as was asked by AxelG, but I think that setting up appropriate groups will be more beneficial. Being able to have different configurations to copy your RAWs to location X, Other to Y and/or JPEGs to Z seems the more flexible thing.
To be honest I’m not even sure if you should include all the available individual formats, having a nice selection of groups should be enough.
I’ll include an image that would show a possible look, using a RAWs only group for this specific configuration:
The above is just an outline of what came to mind and, as stated before, I’m not a developer so I’m only partially capable of determining if this is feasible (I think it should be though). I’m sure I might have overlook something.
Anyway, just my 2c, but maybe this will give some food for thought and can be build upon.