Nationals of ALL but 10 countries will be eligible for airport visa. Many lucky travelers will in fact need no visa (visa-waiver program) at all. These new rules could go into effect in 2-3 months from now!
As for 'Western' nationals, they require no visa to enter Iran if they are perhaps willing to join a tour. if not, they are still eligible for airport visa. All in all, only 10 countries including USA, UK, Pakistan, Aghanistan, Canada? are NOT eligible for airport visa.
There are what Iran VP Ali Najafi was quoted as having said and hence reported by local news agencies. Details are to be worked out though. I will wait to see what (easier) visa rules americans are to be subjected to....because the new Iranian government is interestingly enough very keen on attracting ever more tourists from America! Amir.