I'm not sure a source requirement is particularly meaningful with cultural media. Where should the line be drawn for what is considered source? Does a source requirement demand provision of what ends up on the cutting room floor? I can't imagine this to be the case. If I include 10 minutes from an hour long interview then should I be required to provide the other 50 minutes? How about if I conduct six interviews and only use segments from two of them? Or if it's a musical recording should I be required to include an entire track from the master if I only use one line off it from the second verse? Or if I filmed some footage in 4k, should I need to keep that around -- and make it available -- when I only want to release my project in 720p?

The very process of creating "art" usually entails creation of temporary raw resources, -- templates, guides, palettes, textures, and such -- on the way to producing the final result. Often these resources are disposed of soon after they are created, or at least after the project is completed.

While I think sharing the full details and all of the components of how one creates stuff is fantastic and typically more interesting than the actual result (to me, anyway), doing so is quite a different animal than sharing the finished product. Unless I was sure of the answers to the questions in my first paragraph, I would be rather leery of including material under a license requiring source in my projects.

P.S. Thanks for mentioning Libre Puro. The license in its current state appears to meet my goals, however, the ability to relicense (as mentioned in the preamble) under compatible licenses that allow proprietary formats would seem to defeat that condition.