Canon's S1H is the 1DX.Actually, a 3 series made sense back when the 5D was originally released as the 5D back then was not the high quality camera it became later, being in many ways closer to the later 6D. Historically, the EOS 3 replaced the EOS 5 and sat in exactly the spot, relative to the 1-series, that the current iteration of the 5D sits in.
Putting a 3-series inbetween the 5 and 1 stopped making sense once the 5D got similar AF as the 1-series and the 6-series was introduced (which also pushed the 5D into the higher price bracket where there was previously room for a 3-series). Also, for naming reasons there could never be an "EOS 3D" as that would just be too ridiculous unless it came with 3D capabilities.
Of course, there might still be room for a 3-series. But it's hard to see what might fit in when we do not know what the R1 will bring. Besides, with the price of the R5 as it is and the R1 probably coming in around where the 1D sits...
Speed is the top priority, so I would not expect much over 20MP and 5K RAW for R1.
That is also why I would expect a video-focused R5 to shoot 8K RAW video.