I like this too. But it has the side-effect of the left-hand side of the equation impacting the right-hand side, which goes against Fortran’s philosophy, I believe. In MATLAB, the LHS can change the behavior of the RHS, which is a strange but sometimes handy feature.
Another possible remedy would be to require the compiler to automatically set the length type parameter of all elements to the largest needed. With this rule, the resizing of elements will happen twice: once for array construction and then assign the value to the LHS.