Just cause the ATS system does not do it's part there is no reason for pilots not to try their best to be helpful to other aviators.
I agree with the spirit, DFC, but there is a danger of creating so much noise that it defeats the object. In fact Rule 4 says:
Reporting hazardous conditions
4 The commander of an aircraft shall, on meeting with hazardous conditions in the course of a flight, or as soon as possible thereafter, send to the appropriate air traffic control unit by the quickest means available information containing such particulars of the hazardous conditions as may be pertinent to the safety of other aircraft.
It doesn't say "unexpected" though perhaps it should. I don't think IMC is in itself hazardous and I'm not sure that I'm qualified to say whether it is to be expected by another pilot.
(The original Q, BTW, didn't say that the conditions were unexpected, though it's a reasonable inferrence.)