I wonder. Maybe.
I just think that the way they label things doesn't leave much room for change. Where they think they've honed in on the true nature of something. So the mage would always just be Sarrebas.. the dangerous thing.
True, and the choice to make a young magic sensitive Qunari into a (Qunari word for tranquil) would probably be left up to the Tamassrans. I just think it's something that the Ariqun might want to explore. Yes it's taking away a weapon that the Antaam uses, but even the Antaam seem to dislike using or having Sarrebas around, and they do have black powder which is almost as good. Sarrebas are barely trained and so it's not like they have refined healing or barrier magic, they really aren't all that more effective than black powder canons, no where near what trained mages can actually do.
They may not go for it, but I'd be interested in at least seeing what the Qun's take on tranquility is. If given the option would they choose some more reliable, devout mages to be Sarrebas and some reckless ones to be tranquil? Would the Ben-Hassrath try to use it on regular people that prove far too unreliable, even for alchemy?