He will not be the executive leader. It’s more of a ceremonial position, but nonetheless his election would be a statement by the electorate.
It is mostly just a ceremonial position, but Hofer already said he would consider calling the parliamentary elections early if he wins (one of the few actual powers the Austrian president has). This might allow the leader of his party, Heinz-Christian Strache, to become the Chancellor and have the real political power in the country. Hofer’s win would also send a larger message about the mainstreaming of the populist right in the Western World and the fight against Islamization.