The good thing would be to get a JTV whisper when being close to the limit, or with a server/whisper tag subject like
@type=WhisperLimit;current=45;max=50;reset-at=943753496736934
Or even JTV IRC server sending the remaining ratio in USERSTATE after a message sent, by whisper or not.
I am also awaiting for a clear answer from devs, let’s hope for a simple solution from them