I think it would have been more interesting if they let Alison get away and she becomes their nemesis, using her inside knowledge of how the CIA operates to foil them.
Though I don't think she has enough charisma to be an arch villain that consumes Saul and Carrie to want to get her.
What they should do is find a way to get Tasneem back into the picture in future seasons. She got away with screwing the CIA over and they'd probably want to get back at her. Of course, Pakistan only has limited ways to hurt the US and US interests, unless lets say she had something to do with someone like the San Bernadino terrorist bride.
But Tasneem was a more colorful villain than Alison.
In this season, only Kasim was humanized among the terrorists. The rest were cartoon jihadis. The show did too much with Brody but at least they tried to explain his actions somewhat and show how his family life probably set him off in certain ways.