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.
Bitcoin is becoming more and more popular around the world but we can easily see that governments tend to accept it as an asset, no country wants to turn it into currency and use it to replace its own currency. Only countries without their own currency think of legalizing bitcoin as legal tender but most of these countries are small countries.
With Trump being elected and maybe his administration will be more friendly to bitcoin but don't forget that governments are centralized entities and they will put their own interests first, they don't like decentralization so we should have realistic expectations.