who stated that he will eliminate Trump's tax cuts, raise the capital gains rates and possibly eliminate the step-up on basis of real property?
Is he abolishing Congress and taking over as dictator? The President does not have the power to create laws like that. He may be able to influence Congress to some extent, but he does not have the power to do any of that himself. So if that is what he said, he is just blowing a lot of hot air (like all of the politicians do).
As for any law changes that do eventually happen, *IF* any of those changes that you listed do happen, there is NO WAY they would happen quick enough to happen for the 2020 tax returns.