Asrock had 32gb crucial sticks at computex. Heard they're supposed to be out sometime this year. Also 2666 and cl19
In general nice, more RAM is always great, but on a (very good) two DIMM slot ITX board the RAM speed will be very limited. Short example with an ASRock Z370 ITX and very good binned Samsung B-Die memory:
With 2x8 GB I can easily OC my RAM to DDR4-4500 CL18 stable, booting up to DDR4-4700 no problem
With 2x16 GB I have a very good IMC with my CPU, but still a "wall" at DDR-3733 CL16 (with the best board for RAM OC - Maximus XI Gene - using the same RAM @ 2x16 GB DDR4-4133 CL17 was possible)
So with 2x32 GB anything around ~ DDR4-3000-3200 will be tough if this scales like that before with 2x8 GB vs 2x16 GB.