I really don't understand why Canon didn't continue with high and low resolution 1 series cameras. I can't imagine wildlife shoots other than those in a blind or in a nature reserve, not cropping. It just seemed wrong to not offer 1 series features in a higher resolution body but the R5 is getting closer - no fancy joystick though.I've loved me a few 1D bodies over the years. They were brutes that excelled above the others through the heyday of the 5d3. Critically back then, they also had similar resolution as those bodies they lorded over.
About the time the 5d4 came around, things weren't so clear. It depended on what you shot. Sports photographers and PJs naturally stayed with the 1D series. Resolution above 20mp is somewhat of a nuisance for them it seems. Wildlife people did all sorts of things, again, depending on what they shot. Reach limited guys sometimes used the 5DsR of all things. Some used the 5D4 (I moved to that for the 1.5x resolution and improved sensor). Some went to the A9 (I did that too, eventually, to complement an A7r4 that was dripped with vinegar from 60 megapickles).
So here we all meet up again smoking cigars in the nursery ward of the Canon R5, asking ourselves which would be better: the 1DX3 or the R5; a question that dates us all to the times when people took pictures and didn't care about video and heat whatever the heck vlogging is or was. It appears from what you read on the web that it's only we who care to answer this.
While we can't know for sure, we can surely see that there's very little the R5 can't do that the 1DX3 does, and there's quite a lot it does the 1DX3 can't. Canon being Canon, I wouldn't be surprised if a 1 series in the R format might not do a lot more than give a different form factor. Add some girth to seem girthy, like the outwardly bowed panels on a Ram truck, hiding the small production bits dwelling inside. Slap on the ethernet and other connecting parts that <1/100th of 1 percent of the buyers will ever use. Come to think of it, that could be a good description of the A9II's "upgrade."
To the original person who asked the question, I find myself coming down this way: The 1 series isn't the future. Don't sweat the status implied by slumming with a 5 series, when it beats the pants off the 1 series, at least for now. But do cancel your pre-order for the R5 because I got to watching the vapid Canon video when they were releasing it, and I only pre-ordered 10 minutes in, so there are a bunch of jerks like you in line ahead of me.