Hmm, an interesting prospect and one that is appealing to some because of the tolerance showed by Nader Shah toward the Twelvers. However idk if the Afsharids could achieve a totally different and more Sunni tolerant or Sunni dominated Iran.I feel that it is almost inevitable after the polarizing Safavid rule and the ideology preached by them that it was becoming more and more difficult to rule Iran without being a Twelver. For one thing, I would say that it would take a radically intolerant and domineering Sunni regime (Salafi?) to redo and end the Shia dominance of the area. Tolerance alone will not cut it, with the Twelvers.
However if a longer Afsharid dynasty happened I would suspect them to slowly become more and more like their subjects and this other than going Safavid on them, which won't be easy, is, to me, the only way the Afsharid state could survive any longer than what it did (60 years).