I don't think EB3 visas can go waste in future. It will happen similar to what happened with EB2-C where people downgraded to EB-3. There will be lot more cases in EB-2 than EB-3, very few apply in EB-3 these days.
Even some employers who are applying in EB-3 now to prolong the stay of the employee with the company will then file in EB-2.