Personally, I would like to see the following features: 1) quad-pixel AF; 2) Integrated Vertical Grip; 3) 30-40 MP sensor with excellent high ISO quality; 4) top fps of 25 fps with no drop in bit depth; 5) an electronic shutter with adjustable speed so one can go silent at lower speeds; 6) Spot metering linked to focus point; 7) global shutter to remove rolling shutter; 8) two type B CFExpress slots, 9) Rugged construction and weather sealing similar to 1D series.
To me it's all about AF performance: locking on, tracking, stickiness. Tool in his rushed initial A1 review reports disappointing birding results. The camera needs to be better not worst than the A9.
So, for the R1, 20fps electronic is plenty. Quad-pixel AF if it truly provides AF improves, yes! Read speed has to be dramatically improved over the R5. When the speed of the target speeds up, and moves erratically, the R5 is hopeless. The A9 is almost as good as an OVF in keeping up. I don't know if Canon can design around Sony's stacked-sensor patents--it took long enough for Canon to circumvent the patents that prevented it from improving sensor DR--but Canon needs to speed up this significant juncture.
And let's stay with the type B CFE cards. Two slots preferably, but I can live with one.
Body style is not that important to me except that I don't want a hulking 1DX beast of a camera. If a built in battery grip is required (why?), let's keep the entire package close to the same size of a R5 with optional grip or not much bigger.
I for one, like 45+ MP. When I was still in the Sony camp, I begged for a 36MP sensor, but now that I've seen the A1, I've gotten greedy.
Add the super-fast flash sync for icing, and keep the price under $7k U.S., and I'm there.