Iran is feeling pressure on a number of fronts--the children who have grown up under the Islamic GOI don't have any Shah or Mossadegh references that infuse their daily life, and they don't care about all that "ancient history." All they know is the Guardian Council, the baseej, the ulema, the RGs. They also know the internet, and they want Iran to have more, not fewer, windows on the world. Add to that a crippled economy, which puts extreme pressures on the elites as well as the masses, and that makes for a shit load of people unhappy with the government.
The Guardians, and most specifically, the Supreme Leader, can double down and pretend it's nothing but a thing, but they can't keep this up forever. They know it, too. Hell, they are a major oil producing country and they are rationing and IMPORTING gasoline (which I can remember buying for pennies a litre) because they no longer have decent refinery capability.
This is a case of smiling and accommodating, and the Syria issue did provide a way to the table, but the sanctions regime also played a large role in this rapprochement.
I'm pleased. Iran is a great place to visit; not too safe these days, ya gotta watch yourself and you cannot speak freely at all, but maybe someday that sense of oppression will be lifted as well.