If a hardware hashing device was based around a 10Mhz oven controlled crystal oscillator;  and the algorithm has a time factor built in that can be related/based on this;  it could easily become a standard for limiting hashing speeds;    and could easily be re-verified as to be a valid result by the network using that time-base schism.   It is of-course more involved than just a simple single function;  but if worked properly;  the time function can be integrated at steps throughout the process of calculating.

Example:  Calculate for a result;  and during each mathematical operation;  do a math operation on the intermediate value/variable with the timer's current value as a salt;  do the next step;  salt, etc.   All salt is based on the timer.

This way;  you are forced to conform to the 10Mhz oscillator's salt, and it will disrupt your ability to hash faster as your result won't match someone else that is running the correct timebase, when you are accelerated and hashing faster.