When using the wt_to_mdb_bson python script the expectation is that this will be read by a human being on the other end since the tool only outputs a human-readable version of the BSON.
Processing the output with other tools is somewhat difficult since it involves either reimplementing the same logic or making some ugly hacks to get the required data out.
If instead the script where to support outputting things as valid JSON this would be much easier to do as we can then use standard tools to process the output like jq.
I've attached a patch that modifies the script to output valid JSON by specifying the result to be
{"key": <row key>, "value": <row value>}with a flag.