5,655 AF points = number of AF point positions you can choose from ("But the 5,655 points don't correspond to what we traditionally thought of as autofocus points from the era of SLRs, when phase-detection autofocus systems used separate, dedicated sensors")
AF coverage: RF lenses have 100% vertical and 88% horizontal coverage, some EF-mount lenses will only have 80% horizontal coverage
Canon EOS R AF vs. Canon DSLR AF: "the EOS R would win sometimes and the 5D IV or 1D X II other times"
20mm flange depth choice was made because of "strength and ruggedness"
Not all RF mount electronic contacts are currently used
4k video limitations are because of the "CMOS sensor system".