First of all, it is guaranteed that the SEC chair will be replaced by a new one. Trump has said that he will fire Gary Gensler if elected.
It’s pretty much a given. Any new president will replace officials not on their side, especially appointees. But what will the new SEC chair do for Bitcoin? As far as I know, Gary Gensler was known for saying Bitcoin will never be a currency. So, could the new chair help push Bitcoin to be recognized as a currency rather than just property in the US?
Expecting the US to promote bitcoin as a currency is a very high expectation and I don't think that will happen in any way. The United States dominates the world by forcing every country to use and depend on the US dollar. If they legalize a currency that they do not control, it will negatively impact the dominance of the USD and that means it will directly threaten their power.