A massive negotiated settlement is seeing a number of towns and villages, including two Shi’ite towns in Idlib Province and several rebel-held areas along the Lebanon border mutually evacuated ending protracted sieges on both sides, with some of the locals trapped for over two years.
Resolving the situation in town swaps is highly controversial, with criticism particularly from NGOs that this amounts to forced wartime population transfers and is turning large portions of the country into ethnically and religiously cleansed mono-cultures.
Which is a fair point. The Syrian war has driven Sunni Arabs out of some parts of the country, while Alawites, Shi’ites, and Christians are virtually killed on sight anywhere outside of government territory. The evacuations are an imperfect answer, and probably in practical terms a violation of the Geneva Conventions, but are also virtually obligatory to get civilians out from under protracted sieges.
The same thing happened during the US occupation of Iraq, beginning in 2003, with most neighborhoods in the country ending up overwhelmingly either Sunni or Shi’ite, and any mixed neighborhoods the site of such heavy violence that one side or the other was forced out.
That could be a problem long-term, as in Iraq this widespread displacement was a big part of the rise of Sunni Islamist influence. In Syria, of course, this has already happened at any rate, but sectarian tension is likely to be a long-term issue in the country, even when the war ends.