Vernacular works fine for me. And yes, there can be no hard boundaries. Nearly all sub-genres of vernacular drinks seem to be riffs on classic drinks like the daisy and mojito.
Perhaps any classic drink can be rendered a vernacular drink in unpracticed hands? But that shouldn’t imply that all vernacular drinks are bad drinks, even if a great many are. The most successful ones, I suspect, are simple and economical to compound, and anodyne in effect. For example, they work well out of a pitcher at a party. (I do tend to get a bit grumpy, however, at $15 a pop.)
Are there enough tenets of classical mixology to clearly differentiate it?