There's also the possibility that they will come out with Digic 8+. This has happened several times before, the latest one was the Digic 6+. From my understanding the + versions were all die shrinks, which led to the chip performing faster (due to higher clock speeds) with less energy consumption.I doubt it will have dual digics unless it's a 1D form factor with a battery to match.
this is just pure throughput not even talking tracking.
the 7D Mark II only had a throughput of 200MP/second and it even had dual digics to try and do that with. one DIGIC 8 chip is 20% faster than the dual 6 DIGICS in the 7D Mark II.
In addition I am 90% sure I remember reading posts where the issue with 8 frames per second on the R was more a limitation on the speed of the sensor, not just the digic chip's processing, and that the tracking speed limitation was a combination of both with potential room for optimization. I remember these conversations were more applied to video but high FPS with high pixels would also be in that boat. A greatly improved readout speed means the digic chip can start working on the issue faster, so with a brand new sensor design we could see some improvements in total throughput even without adding a 2nd digic chip or even upgrading the design through a die shrink.