Q: When will OSX El Capitan Support the Canon 5D Mark IV RAW files ?

This is a users forum so we have no insight into what Apple's plans are.

What dialabrain said.

This is a brand new model, so it is natural that raw support is not yet in. Updates that support raw formats for new cameras are pretty common, so hopefully it may not take long (this is a user opinion, based on past experience; no inside knowledge).

When the 5DMK3 came out it took some time (6/7 weeks) for it's RAW files to be compatible. I'm shooting both RAW and JPEG at the moment. When I need the RAW version I use the canon softwear to create a TIFF. It's not great and its a slow work-a-round.