I wonder why they would limit themselves to 30 FPS if the sensor is just 24 MP. 30 MP 30 FPS would have matched the R5 in terms of data throughput. To do that with 24 MP, the camera would have to shoot 37.5 FPS.
What's the bottle neck? The stacked sensor should be plenty fast, and we know the processor can handle more data. Perhaps they just don't want to overwhelm the buffer, as the CFexpress cards can't keep up with this much data and therefore endless shooting like on the 1DX III isn't possible.
Honestly, I was thinking about this all day.
I was just looking at the buffers of all the recent cameras on The-Digital-Picture:
Perhaps at 24 megapixels using the CF Express Type B Canon can ensure a 1000+ image buffer at full-quality, full-resolution 14-bit 30 FPS? I think there's a strong case for 30 FPS at 24 megapixels in that scenario. The A9II only has a 361 image buffer, and I honestly think the moment a former 1-series user hits a camera's buffer, they're going to wish they were using their old 1-series.
It also could mean that the camera has more processing power to ensure a super responsive, zero blackout, 240+ fps viewfinder throughout shooting 1000+ full resolution images. Reliability and responsiveness is probably the number one request from most 1-series users, and I will say that sometimes the R5 does get a little laggy when you're shooting huge 20 FPS bursts.
Add to that, 24 megapixels would be less of a drain on the battery life.
All that said, I think there's a lot left to know about this camera even if it turns out to be 24 mp. I'd be interested to see the battery life, viewfinder buffer, responsiveness, and any other new features they pack into it before I dismiss it at all.