It's complicated...! 
I have been a Nikon user for many years (since 1984- prior to that I had a Pentax outfit). Since 1984 I have purchased many lenses (AiS first, then AF-D lenses). Only DX lens I own is a Nikon 17-55mm f2.8. I didn't purchase all my Nikon stuff at one specific time though; it took around 30 years or so!
My current Nikon DX bodies are used mostly by my photo club kids (two D1X's, four D200's, four 28-105mm f3.4/4.5 AF-D's).
Some time ago I was looking for a lightweight travel camera, so I purchased an Olympus EPL3 (hated it, melted the first week of owning it). Purchased a Panasonic G3/two-lens outfit, but I never really cared for the images I got with it (too pixilated, smeared details even at lower ISO's). Then got a Canon T3i/two-lens outfit for travel (bigger sensor than the G3). Soon after I got a Canon T6/two-lens outfit because it was on sale and was lighter than the T3i. Then Amazon had a sale on the Lumix GX85/two-lens outfit...another attempt at the illusive "perfect travel camera".
I decided it was time to upgrade as I was shooting mostly sports (non paid work). Nikon had nothing to offer (only the D300S at that time). So, I decided to plunge into Canon with a 7dmk2, 16-35mm f4.0L, 70-200mm f2.8L. Two months later Nikon released the D500. Had I known that Nikon was going to produce the D500, I would not have purchased that 7dmk2. This thread would not have even existed because I would have continued using Nikon.
Then I purchased a Canon EF-S 17-55mm f2.8 because it was on sale. (Comparable to my Nikon 17-55mm f2.8 AF-S DX)
Fast forward a year or so and I spotted the D750 on sale. I thought it would be nice to have a full frame body to use with all my Nikon lenses I have accumulated since 1984.
A freak cycling accident back in November caused me to give up mountain biking, so I sold my mountain bike. With that money I purchased a new Nikon 55mm f2.8 AiS Micro. I got a bad copy, so I returned it to B&H and requested a gift credit as I knew I was going to eventually buy something photography related from them anyway. Almost immediately I noticed they had the Canon 6dmk2 on sale!! I went to my local BestBuy and tried out the 6dmk2 and the RP side by side. I loved the feel and look of the 6dmk2 in my hands! Researched a bit more and decided it was a better camera than the RP for my needs, so I purchased it from B&H.
I have only owned the 6dmk2 for about a month now. I have been using it side by side with my D750.
Yes, it is mind-numbing having to go from one camera to the other; both cameras have controls in different places, even mounting the lenses is opposite! Absurd as it may seem, I actually enjoy the challenge. It keeps my mind sharp... 
I enjoy sports photography, however I am frequently asked to do portraits and weddings (been shooting weddings on and off since 1985). At some point I would like to get a 300mm f2.8. I would hate to spend money on a lens like that to then find out (like my luck in the past has proven) that it can no longer be used on newer bodies.
Yes, Canon has an adapter that can fit EF to R, but I'm sure Canon is going to produce a 300mm f2.8 R in the near future. It would not be a smart idea for me to spend a small fortune on an EF now if everything will change in a year or two to R.
As for dumping all my Nikon equipment, that would make sense. However, Nikon seems to be committed to continue to produce F mount lenses together with Z mount lenses. The big question then is will that really even matter if Nikon goes out of business? Also, I get crazy sharp images with that D750 and all my old Nikon lenses! Way, way sharper (pixel peeping) than my 6dmk2. Colors are nicer with my 6dmk2 though...
All this is speculation on my part. I just don't want to invest more money on a dying system (EF or F). Don't get me wrong, I love both my Canon and Nikon outfits, but I'm not ready to take the plunge into full frame mirrorle$$ at this time.