PJRC has announced their "Teensy 4" board.
This is the size of of the teensy 3.2, but features a 600MHz Core-M7 cpu, making it about 5x faster than the Teensy 3.6 (previously the fastest microcontroller-based Arduino...)
And, apparently, hardware support for double-precision floating point.
So tempting, but I see that it has no DAC outputs. I was all ready to order 6 of them to play with, but canceled when I realized it is DACless.
I suppose adding a peripheral to one of its many busses would work, but I don’t feel inclined to pursue that route. I’ll stick with the Due.