I would also appreciate this feature request, and wouldn't mind if a dev could chime in to say why it isn't possible or why it's difficult to implement?
I posted a question in General Support trying to do the same thing before I realized it's not possible:
http://forum.kodi.tv/showthread.php?tid=238709
I've created custom menu buttons in Aeon Nox for "Docu" and "Stand Up" because I want all my Documentaries and Stand Up comedy grouped together. Currently I'm using smart "movie" playlists in this sections for the movies only because I cannot combine the TV and Movies together, but I have Docu and Stand Up stuff that are TV show based.
I've tried "Mixed/Movie/Shows" playlists with both paths and "Mixed/Movie/Shows" playlists trying to group other individual playlists ... nothing populates everything.
If we've already added the paths and picked the correct scraper in our sourcessection , why can't they display together? Combining seems like it would just be combining the actual display function ... is the playlist type linked to the scraper in the back-end somehow?
Either way, I'd love the feature, and understand if it's not possible, but it would be great if someone could shed some light on why it's not possible, since it seems like it should be something that's easy.