I've worked with source maps for a few years now. I've contributed to several compilers and worked with source map issues on them, such as [reworkcss/css], [postcss] and [CoffeeScript]. I've also contributed to [mozilla/source-map].
I've thought a long time about proposing an alternate, human readable format to complement today's (version 3) format. You can read all about it here:
The above link also contains real-world testing and practical examples of the proposed format.
I'd love to hear somebody else's opinions, thoughts and feelings on this!