If the EVF and fps don't get any better (in the next year) then dual slots is the least of your worries for those yearning for a Pro R model. Then again, we come full circle to 'What makes a Pro body' argument again. Seems like over and over the 5D4 is the solution and winner for many not getting the tidbits they cry for from Canon. But alas, people have to have new toys.
In my view the world is a world of compromises - and depending on your application you have to choose the best of those compromises.
I ordered the M50 to try a mirrorless with EVF and it was way better than I expect. The OVF IS clearer, crisper, shure. But the DPAF in combination with EVF lets me choose AF points with a vast amount of freedom compared to SLRs which is - for me - a significant upgrade compared to SLRs. And I never got such a high hit rate with EF with any SLR I used for medium slow applications: predictable accurate AF @f/1.4 in the close focus range with EF-M 32 . While not being a Pro I see professional photographers who might profit from that behaviour with EOS R cameras.
For sports or bif or other "faster" types of photography the M50 is not well suited, just the SL2 was better there. So this might be the domain of DSLRs at least in Canon land for the next year or two years.
But I am shure Canon is working with high pressure on a "Pro level" ML body including some surprising USEFUL features - not only for Canon users. Just my feeling, don't have any information.