Did any developers try data processing out with files which do not represent audio or video contents?
Was it tried already to parse source files (according to selected programming languages) by the means of GStreamer pipelines?
How will an information source like “Table of Other Types” evolve further?
not sure about what you want to do. You can use discovery in Streamer to check out if files are audio or video files or not.
https://gstreamer.freedesktop.org/documentation/pbutils/gstdiscoverer.html?gi-language=c
Can you imagine that data processing can occasionally become more interesting together with additional data in other file formats (besides audio and video)? 
Would you like to handle any contents from tree-like data structures by the means of GStreamer pipelines?
Yes, GStreamer can be used to handle other data formats that are not audio or video related. Most notably this has been used by LIGO for gravitational wave analysis: https://lscsoft.docs.ligo.org/gstlal/
How much can such special development approaches influence related software areas?