There probably will not be a M6 Ultra but we might get a M7 Extreme (double the M7 Ultra) with more than 2 TB/s Unified Memory bandwidth.
I am an independent chip designer myself[1] working on a Wafer Scale Integration with 46.3 trillion transistors (11 times more than the Cerebras WSE-3). Still, I can learn a lot about low power transistors from Apple M6 and A20.