Eyetracking is the reason why ,after the R3 got launched, I didn't buy the the R5.
I too was impressed with the R3, not only by the eye-control AF, but also by what I think are the best ergonomics on the market. Sadly, it doesn't fit in my carrying system, the R1 won't either.
The best of both worlds, for me, would (will?) be the R5 with eyetracking AF, so, the R5 II.
And I'm d*** egoistically happy it comes ahead of the R1!