Thinking about this a bit more...
Honestly I'm a bit surprised at the feature set being discussed. I would sort of expect a camera at this price point to have several of these features nerfed - like no 180 FPS, no oversampled 4k60 (honestly would expect no 4k60 oversampled or otherwise), and no 40 fps ES photo burst. I guess kudos to Canon for including these features.
That said, I bet there will be several things missing/lower-spec'd that will make this camera less suitable for pro work that the R6ii/R6/R5 bodies are targeted for:
- Single card slot (as mentioned above)
- No built-in EVF (mentioned by several others)
- No rear thumb dial or joystick.
- Fastest shutter speed 1/4000 (for mechanical, ES goes to 1/8000 or 1/16000)
- Slower flash sync speed (maybe 1/180 - same as RP) (1/200s in EFCS vs 1/250s for the R6ii)
- Lower burst rate with mechanical shutter - maybe 5 or 8 fps. (6fps)
- Smaller battery
- Minimal to no "weather sealing" ???
- No place for your pinky
- Maybe this one overheats in 4k60 considering the smaller body. ??? (Has a 30-min recording limit in 4k60 while R6ii does not)
Things they could nerf that I bet don't get nerfed:
- Probably no artificial record time limit (since the R10 doesn't have one). If so, that would be great and a sign that Canon is done with that silliness. (sort of - 2 hours in 30p, 30 min in 4k60 which are not limits on the R6ii - not as bad as it used to be and much less likely to be an issue)
- Probably has the new multi-function hot shoe (again, since the R10 did). Makes me wonder if the EVF-DC2 physically interfaces with the new multi-function hot shoe...
Finally, things that may get nerfed for no technical reason that would sort of show that Canon is still trying to protect/differentiate the value of the R6ii:
- High-Frequency Anti-Flicker ???
- Burst mode with pre-shooting ???
- Focus Bracketing ???
- A quick video/photo mode switch with retained settings in each respective mode. (has it, not sure about retaining settings)
- RAW output over external HDMI (maybe this doesn't even have an HDMI output). (not supported on R8)
Overall, if this ends up being the same sensor as the R6ii (which is a pretty good sensor only bested by the R5 and R3 among Canon cameras) in a package more like an M6/M6ii, then at $1500 it is quite a good value - compelling for more casual use. Also really interesting for more straight-up image capture - things like timelapse and for use in astrophotography (where it's helpful to have a less massive camera).
Note - everything I've said above is pure speculation. It's fun to guess and then see how wrong you are about it a few days later when the full specs come out.