Industrial diamonds are now made synthetically, but I don't know if the synthetic ones can yet compete pricewise.

They certainly can compete pricewise. It is on quality that they may fall short (although the gap is not large).

The biggest threat to the price of diamonds is not the improvement in synthetic ones, but the sheer abundance of natural ones. deBeers has been fighting a rearguard action for years, maintaining an artificial scarcity by buying up most of the world's diamond prduction every year. But their position is increasingly unsustainable.