jim quist wrote:
...why I would be head over heals in love with a mirrorless camera?
Well, according to Canon their new EOS R's autofocus is the fastest in any camera. There are 5600+ AF points that cover almost the entire image area and it's able to focus down to -6EV (compared to 61-points, -3EV in 1DXII). It's also 30MP (versus 20MP in a 1DXII). The electronic viewfinder gives you immediate exposure preview and make possible to see in low light conditions, too. If you have any manual focus lenses, you'll like it's Focus Peaking, too. The articulated, 2 million dot rear screen might come in handy sometimes, too. It also can shoot silently, since there's no shutter or mirror slapping around in there. Plus the EOS R costs more than $3000 less than the 1DXII, leaving money to buy that RF 28-70mm f/2 lens! The EOS R is a bit smaller and lighter too, even with the BG-E22 battery grip.
Of course, nothing is perfect. The down side is that the EOS R will only get around 400 to 600 shots per battery charge. It's EVF acquires its image from the sensor and both the screen and the sensor remain active continuously while using the viewfinder, which puts a heavy load on the battery(ies). The 1DXII probably gets at least 4X more shots with a charge, though to do so it uses a much larger battery. There's a battery grip available for the EOS R, doubling it's battery capacity. And it uses smaller LP-E6N batteries, which cost about $65 each. That's $100 cheaper than the large LP-E19 pack the 1DXII uses... though of course you'll need more of the small batteries. The EOS R only has a single SD memory card slot and doesn't have anywhere near the frame rate of the 1DXII... only about 8 frames per second (versus 14 with the 1DXII).
And all your EF lenses will work just as good on the EOS R as on any other EOS camera, via an adapter. While I'm not a fan of adapters (they sort of defeat the size/weight savings of mirrorless, which isn't all that much with full frame anyway).... have to admit that Canon made clever additions to theirs. They offer three different adapters... a plain one, another that has an additional control (similar to what the RF lenses have) and a third that's able to use drop in filters (choice of circ polarizer or variable ND initially.... hopefully they'll eventually offer a drawer for screw in or gel filters, too. I notice that several companies have begun introducing various adapters for vintage SLR and rangefinder lenses, too.... Bet there will be a lot more of those for the RF mount in the future.
You might find this interesting...
https://cameradecision.com/compare/Canon-EOS-R-vs-Canon-EOS-1D-X-Mark-II You also might read the EOS R reviews. There's a lot of discussion of possible RF lenses on Canonrumors.com, too.
Personally I prefer using an APS-C camera for sports, and for now there's nothing in the Canon mirrorless line-up. I still might get an M5 soon for street photography, portraits and general fun... but it's not a "money camera", so lower priority for now.