I currently use the Olympus EM1-2 and mainly shoot with only 2 Oly lenses: 12-100mm f4 (24-200 f8 EQuivalent) and 300mm f4 (600mm f8 EQ). I want to buy into a new FF system so that I can get a larger sensor and a good portrait lens with large bokeh (larger than I can get with the Oly 45mm f1.2 (90mm f2.4 EQ) ) at a reasonable size (not a huge & heavy brick). Access to other great lenses to expand my collection in FF instead of M43 is a plus.
Currently the best choice for me for this is the Sony A7R3 with the Sony FE 85mm f1.8 lens. It's light weight, lightning fast AF and I'm happy with the large bokeh. But I shoot half of my pictures in portrait mode at waist level with the LCD screen pulled out in portrait mode - the Sony A7 series can NOT do this. So I'm waiting for a FF camera that can.
The new Canon R lens can! This is really important to me (but I rarely see anyone else care about it). However, if it is true that the Canon R does not have eye AF and does not have IBIS then I can NOT consider buying it. I rely on eye AF as well as IBIS (coupled with lens OS) which on the E-M1 2 with both of these lenses is truly incredible! I won't lose that ability and will wait until a FF system comes out with it to make me happy.
So, I will wait to see what the 3rd player (Panasonic) has with their introduction of FF soon. If it has the fully articulating screen, eye AF and IBIS then I will see what else it has. Maybe it will be the right choice with no other deal breakers. FWIW I really want a big beautiful EVF, and would love to have a 105mm f1.8 lens at a moderate weight. Other FF lenses would be great, but nothing will match the 300mm f4 (600 f8 EQ) lens with the IBIS & OS at a weight & price I can affort - it's truly amazing). I would also like to have more easy to use dials (for aperture, shutter speed & exposure compensation) and a simpler & more intelligent menu system (both the Oly and Sony menu systems are very poorly written). And if you really want to solve the issue of how to focus, then put a sensor in the EVF to track the user eye so that they can look at the image and push a button to indicate what to focus on and track it while I recompose the image and then take the picture.
So I'll be a 2 brand shooter when something better comes out. But, sadly, it won't be the Canon R system with this camera. I really wish it could have been. OK, Panasonic, maybe you'll read this and consider it.