By the time Washington ascended the Presidency Benjamin Franklin was unable to walk because of severe gout, suffered from syphilis, was likely going senile and blind. He was so infirm that he had to be carried into the Constitutional Convention on a sedan chair. Robert Morris complains Franklin, as President of Pennsylvania, left all his responsibilities to the state General Assembly. This is hardly a good track record.
Assuming Franklin miraculously manages to survive until 1792 he will not be doing any governing. What we will see is a United States where the President is more a figurehead and rubber stamp to powerful Congressional leadership. There will be nothing "policy wise".
I agree that he had physical infirmities, but I haven't seen anything to indicate that he was significantly less mentally sharp in 1789 than he was a decade or earlier when he was navigating the diplomatic back channels of Europe excellently. Can you please provide references?