No. Because they want people transitioning to mirrorless to go with Canon. So if they wanted to target the same market as the Z9, A1, 1DX 3, etc, why not just release a camera that belongs to the 1 series in all but the name?
Why use a slow SD card slot, forcing users to chose between speed and redundancy?
Why leave out spot metering linked to AF point?
Why use the R5 12 FPS shutter, when the 1DX III 16 FPS one was an option?
To me, those are hints that Canon tried to reduce the cost of this body by explicitly not designing it as a flagship, nor as a temporary offering.
I just don't see how it makes sense to develop a completely new camera to make it seem like they have a competitor to the Z9, when the R1 is less than year away anyway. The resources spent working on the R3 could have been used to accelerate the R1 to some degree.
I can totally see the R3 being the only one of its kind if the post covid market doesn't work out the way Canon envisioned it. But I don't understand how it makes any sende to buy extra time for the R1, or refine its technology, as you put it.
So, first off, let me say, I suspect you are correct and that Canon will both keep the R3 line and introduce an R1. But, I am not completely sold on that idea, Matter of fact I am probably 60/40 on it. Why? That would imply that there is a big enough market to support two "high end" camera body systems with integrated grips, etc. Ever since the 1DX, Canon has not done this. Nikon has not done this, and Sony is close with the A9 and A1. If Canon does keep both the R3 and introduce a R1, the A9/A1 is probably the closest allegory...but I've also wondered if the A9 is going to go away and be replaced by the A1.
So, to answer the questions you pose, I'll play a bit of Devil's advocate, but it isn't hard to see the otherside:
why not just release a camera that belongs to the 1 series in all but the name?
Because the 1DX III was released just the previous year and they wanted to give it a bit more time "as the flagship." Plus there may be tech Canon wanted to further develop before introducing it in an R1.
Why use a slow SD card slot, forcing users to chose between speed and redundancy?
Differentiate the R3 to the 1DX III, not just a future R1. Plus CFe was very new when Canon was likely making decisions...perhaps they were concerned about potential CFe card supply and didn't want to leave their cameras stranded.
Why leave out spot metering linked to AF point?
The 1DX III has a completely separate sensor and a separate processor for AF and metering. The R3 has to pull all that information off a single sensor. Could be the processing power/circuitry is not there yet.
Why use the R5 12 FPS shutter, when the 1DX III 16 FPS one was an option?
Canon has been clear that they think of the R3 as an electronic shutter first camera. I really wonder if the R1 will be shutterless. This could also be used as a reason for the R3 being a placeholder. A step to wean people off mechanical shutters. Why 12 FPS? Likely to save costs as it might be the same/similar shutter (or shutter tech) as the R5/R6. And, this is just something I marvel at, but think about the AF issues with the mechanical shutter when you AF on the sensor. You cannot AF while the shutter is closed! The R3 AFs 60 times/sec. How much is 12 fps a function of the actual shutter speed or a function of allowing time to AF with the sensor. The shutter is likely blazing fast. Also, the 1DX III is their current stated flagship, this is still a point in favor of it.
But I don't understand how it makes any sende to buy extra time for the R1, or refine its technology, as you put it.
So, basically, if they aren't going to continue with the R3, why not just take the exact same body that is the R3 and announce it as an R1? Part may be to give the 1DX III some space. But in terms of tech, think about your spot metering example, what if that really is a processing power limitation and somewhere in Canon there is a spec sheet that says "no 1 series camera shall exist without spot metering linked to an AF point" but yet, the processing power isn't there yet (think about it, the same circuitry that still gives us some rolling shutter is now also being used to AF/AE). Maybe they want flash sync speeds of 1/250th or something else. But, the flipside works here in my mind....if they had the tech they wanted for an R1 developed, why did they not release it first rather than the R3? Only reason I can think of is they wanted those that favor less MPs to know they'd have a mirrorless successor before introducing a large MP camera....but if the R1 tech is ready.....