It makes a lot of sense for Canon to develop the 1DxIII alongside the Rf variant. Cross feeding the tech and needs, spanning the dev across two cameras. It bodes well for the Rf mount in general but it's a snub to the 5D5 hopes. The 5D3 and 4 were co-developed with the 1 Series cameras. I dare say that the 5D5 will be co-developed with the Eos RII which will probably improve the R series substantially, but devalue the 5D5 somewhat. Canon have never really understood the market needs for a 5 Series. It took Jeff Ascough's inspired input to get the 5DIII spec from the weird spec of the 5DII. Canon likewise didn't understand what the market wanted with the Eos R....not even close. A great little camera, but shameful compared to a 5D4. Baring in mind that there are more 5D's in the hands of pros around the world than all the other camera brands and models combined.