if you do that your steps will no longer meet code, plus you will have to cut all your door jams higher. years from now when all that flooring is removed the jambs will be 1-1/2 or more above the floor. if you have to trim the doors also then those would need replaced also or be 2-3 inches above the floor. nailing to hardwood that moves when it expands and contracts is just asking for trouble. if you want to do it twice then just nail over the existing.