@serhiy.storchaka while you are doing your overhaul will you please add support for raw json values. I often find myself where I have a serialized object that I want to include in an object response that I'm about to serialize anyway. The implementation should be very simple. Here is my workaround code:

class RawJSON(str): pass

origEnc = json.encoder.encode_basestring_ascii
def rawEnc(obj):
  if isinstance(obj, RawJSON):
    return obj
  return origEnc(obj)
json.encoder.encode_basestring_ascii = rawEnc

https://stackoverflow.com/a/48985560/289240