To give a counter voice to Max' answer, I actually think that online booking will be available very quickly. Not for large hotel chains, but for services like AirBNB and Hostelworld. Plenty of Iranians have accounts abroad but now, American law no longer prevents American businesses from doing business with Iran.
I'm not sure if the link will hold, but some properties seem to already be bookable online. Here's one.
As far as international banking is concerned, I'm reasonably sure that the Iranian banking system has been connected to the rest of the world for years. The connection could just not be used because of sanctions.
So, here, too, I think things will changes reasonably quickly. Credit card payments within Iran might take a bit longer to get off the ground, but using ATMs with foreign cards will be available sooner.
My estimate is that, before the end of the year, some ATMs in Iran will work with international cards and most big cities will offer competitive accommodation that will be bookable online.