This idea of moving (forcing) different ethic groups around to form a homogenous state has been tried, e.g. former Yugoslavia, and doesn't work, with disastrous consequences.
Also re. Mariupol, you build the cheap flats, but what are people to do there? The main employment was at the steel works - apparently the largest in Europe - which has been destroyed along with the town's infrastructure.
I think this is simply another publicity stunt by Mad Vlad for home consumption.