He certainly could one day if FnF are released from conservatorship and allowed to be the companies the were pre-2008. I have seen an interview where Bill Ackman was asked if he had any political aspirations. He said not really, but he does enjoy politics and has many friends in DC. He jokingly stated that if the POTUS is like the CEO of America, he would rather be the CFO. Actually running the business of the USA.
If Ackman does get a seat on the BOD one day, rest assured he will want at least 2-4 of his cohorts on there with him.