I davened at a shul this morning that announced mincha at 5:30pm with maariv following immediately after. Plag mincha is around 6:45pm today. I pointed this out to the gabbai and he said that there is an opinion that says that you can daven maariv before plag, and that it is ok in this case because otherwise the attendees would not daven maariv at all. I didn't argue with him, though based on what I have learned, you can't daven maariv before plag (and thus if you do, birkot keryiat shema would be ברכות לבטלות, not to mention that tefillat amidah is also לא בזמנו and is at best a תפילת רשות).
Does anyone know of a legitimate source permitting this practice (davening maariv before plag, specifically for those would would otherwise not daven maariv at all)?