Machinekit would either have software step generation (with RT-PREEMPT) kernel, or depending on platform the hardware taking care of this by PRU (microprocessor) on a Beaglebone, FPGA on a mesanet pci card / De0 nano soc.
As long as you have the motors driven from the same board this is not really a big thing because you’d have the interpolation done by a HAL component. Then the HAL component sets the velocities, etc. Where movement (rough interpolation) is planned by ROS.
Synchronized moves from different Boards is not available (not yet anyway; execution of the HAL function thread needs to be done from an external source (like a hardware interrupt from fpga), there’s been a bit of experimentation with NTP server in the past, but I don’t know the details)