I was a RO research chemist for about 10 years. Developing a membrane is one thing, but finding a good support system to keep it intact is another whole project in itself.

Most common is the use of non-woven fabrics made out of synthetic materials. The difficulty in scaling up is finding a fabric that is consistently smooth without any loose strands that protrude up through the membrane (a loose strand causes a leak). And the larger the piece you need the more difficult it is to manufacture consistently.

Since the graphene membrane is supposedly only an atom thick this is going to be extremely difficult. It may be many more years before they find a solution.