A cleaner/safer solution here would be:

  tok, *remainder = _wsp_splitter(value, 1)
  if _rfc2047_matcher(tok):
      tok, *remainder = value.partition('=?')
      
where _rfc2047_matcher would be a regex that matches a correctly formatted encoded word. There a regex for that in the header.py module, though for this application we don't need the groups it has.

Abhilash, I'm not sure why you say the proposed solution only works for utf-8 and 'q'?