To be honest, to be fair, and to be logical is appropriate phase Iran needs to go through when buying a re-purposed inventory before going all-in with new aircraft. The Nuke talks need to succeed for both Europe and North America, before even looking at an order book. If all goes well during a treaty signing for concerned factions then its back to catching up with the travel industry. Brand new equipment for Iran would be a disaster after flying 40-year-old aircraft. It would be as if everyone in Cuba gets a hybrid car without an owners manual.
The Iran talks will do more than just stop insane aspirations for nuking the world on religious principals. It will turn a trade conduit into a flood of Hybrid airplanes totally different than its 40 years old 747's it has in its fleet. Iran will need to develop its airplane infrastructure up to the 787 level of operation before buying that class of airplane. Even the A-350 would complicate Iranian operations to extent of missing some operational points and flying policy for operations. It would be better if they would order the 767 or A-330's for fleet renewal in the first five years and learn how to efficiently operate a solid standard, before leaping at the all new formats found in the duopoly's newest aircraft. Buying used is a high priority when renewing its commercial fleet.
However, pride once again influences decisions. A dual approach for Iran's new found purchasing access should not be hurried nor should it be an archaic expression for quality. They won't go old as in well just keeping old airplanes. They have an opportunity to buy recently replaced equipment from other airlines which has more life and value than what Iran needs for a fleet in the near term. I see the country seeking a middle ground in the purchase arena. Buying what it needs from used inventory for a fast start-up, and then placing orders at the same time anticipating they are at the back of the delivery line for the latest technology aircraft. Iran would expect to catch-up its operations during its transition from 1970's to 2015 during the next 10 years.
Iran is in a good place with so much used airplane inventory available for them to acquire at bargain prices where it may build its personnel up with relatively new equipment while waiting for Aircraft like the Max or NEO. It all depends on this Nuke negotiation currently under consideration. Iran's future is in its own hands at this time.