Some plug-ins, such as the Theory plug-in, enable users to create new operators. However, it is not possible to overload existing operators. For example, a user defining type for real numbers can't define an operator + on reals as it is already defined for integers. This causes libraries to define operators with some unnatural and quite arbitrary operator names for common operations.
Allowing operator overloading could make things more readable for users. However, it will require some significant changes to the parser and type-checker.