Nvidia did not say it will be a hardware limitation. In fact, they will almost certainly implement it in software. For example a "Lite Hash Rate" card will probably have a bit permanently set to 1 in the firmware/eeprom. The driver will read the bit, and arbitrarily enforce the restriction on such LHR card. This solves potential legal issues of retroactively crippling cards already out in the market, since only new cards sold from now on as "LHR models" will have the bit set to 1.

But miners will find another software hack (just like they did for the RTX 3060 earlier) to bypass the restriction.