I don't believe that reconfigure is sufficient, no. My understanding is that it will not trigger decodebin to remove elements from the pipeline; it will only ask the existing elements to change what they are outputting. For a decoder, or a transcoder like videoconvert, this is sufficient to change the format from e.g. one RGB format to another, but I doubt it will be sufficient to change whether a decoder is in fact decoding or not.
OK, so we still need to recreate the pipeline. Do we recreate the whole wg_parser or only recreate decodebin pipeline?
Another question: if we assume that the caps configure only happens during setting up the reader, before decoding anything, and ignore the mid-stream situation for now. Do we still need to do the recreate things when caps configure happens?