There are definitely pros and cons to HCA’s, as the impassioned discussions in the lower mainland last year regarding Vancouver’s first HCA in Shaughnessy demonstrated. However, the idea isn’t new, as I learned with a bit of research: a few years ago Ottawa created a Heritage Conservation District in Briarcliffe, a community of 23 mid-century modern homes, the latest of several in that city. 
Other cities across Canada (including our neighbour Victoria) have done the same. There are certainly challenges to creating and keeping these areas as intended, even more so today as pressures to rezone and rebuild increase, but in my mind definitely worth the effort.
Sidenote:
Vancouver Heritage Foundation has a great resource page about the HCA: http://www.vancouverheritagefoundation.org/learn-with-us/understanding-the-heritage-action-plan/