Waibo leaker E8M_8888, who is often right in advance, has released a set of presumed specifications for the upcoming EOS R1.
Although this camera will most likely not be marketed by Canon as a dedicated cine model, as a flagship model it is just as likely not to be limited beyond measure in its cinematic possibilities.
A 30-megapixel full-frame sensor is said to be installed, which should offer extremely short rolling shutter times. The extremely short flash sync time of 1/1250s provides an initial indication of this, which would correspond to a sensor readout time of approx. 0.8 milliseconds without any further tricks. However, this would be an almost unbelievable value for a rolling shutter.
Further indications of a fairly fast sensor are provided by the rumored RAW continuous shooting functions: There are said to be unlimited continuous shooting at 40 frames per second (1:2 CRAW) and up to 60 frames per second (1:3 CRAW), from which you can see that the compression write rate is still the limiting factor here. Time-limited continuous shooting should be possible at up to 240 frames per second, which would mean a maximum rolling shutter readout time of 4.16 milliseconds. This would definitely be within the capabilities of current sensor technology.
However, the integrated video modes themselves do not go that far:
At full sensor width, 6.7K with a maximum of 60p should be possible in 12bit Cinema RAW. In addition, 12bit Cinema RAW with 120p4.2K should be possible in an APS-C window.
If you record in an internal 10-bit codec, 4K120p should be possible in several possible variants: full frame/APS-C-DCI/UHD C-log2 & C-log3.
The estimated dynamic range of the EOS R1 has already been stated elsewhere by E8M_8888 as an astonishing 15.5+ f-stops. This would pretty much match the dynamic range specs of a 
Canon sensor introduced in December.
It remains to be seen whether this will all turn out as speculated here. However, such camera specifications are definitely within the range of what we can expect from large-sensor DSLMs in 2024.
;)