turkey would be a good candidate for regime change but the dynamics are more complicated and this is unlikely to be a realistic policy decision.
an operation like this might work in dismantling the new fascist regime in syria, which replaces a moderate one, which fell in a moment of poor decision making by the russians. it was a mistake for the russians to let syria fall. however, syria will need time to build the kind of serious democratic opposition to fascism that already exists in iran, after 45 years of resistance. the situation in syria for many years was such that socialists and secularists did not mobilize because it was more strategic to back the assad government as a lesser evil, as they were fighting the islamists. now, syria will need to build a resistance against fascism. that resistance should be supported when it develops.
there is currently no substantive resistance against the fascist saudi arabian monarchy to support. the resistance in egypt and algeria needs to be rebuilt. libya was one of the most progressive states in the region before it was attacked by a psychotic lunatic named hillary clinton that sadly destroyed it. there is no resistance left to support because the americans destroyed it. it will need to develop as well.
in iran, there is a resistance and there is revolutionary potential. the conditions are met for revolutionary overthrow, and the international order should support that revolutionary overthrow or itself be reformed so that it does.