Yes I'm pretty sure the DIGIC 8 doesn't do anything to the RAW file, why is that a safe assumption? Because Canon only ever claim improvements on the OOC jpegs. I don't have a clue what criteria Canon have for setting the highest rating for the ISO, but 32000 - 40000 is 1/3 of a stop, hardly anything worth writing about.
Nevertheless I'd like to know where, exactly, people think they are seeing an improvement, because I have not seen anything that makes me think "a 5D MkIV couldn't do that". Not that I don't find may of the features of the R system interesting and improvements, just that IQ isn't one of them.
I very interesting comparison is going to be a 5D MkIV with EF 50 f1.2L and the R with the RF 50 f1.2L, as far as I can see Canon are saying the big IQ improvements are because of the optical freedom that extra 20mm gives them. Lenses are the difference, not the sensor or processor, for RAW files.