This isn't quite what you asked for, but I've run into problems where the distinction between scalars and 1x1 matrices was important. iirc, something like

This isn't quite what you asked for, but I've run into problems where the distinction between scalars and 1x1 matrices was important. iirc, something like crossprod(y, crossprod(A, y)) * V where A was nxn, y was nx1, and V was an arbitrary matrix throws an error while drop(crossprod(y, crossprod(A, y))) * V works.