Создание пользовательского класса QPointF

Да, вы должны перезаписать методы __add__, __mul__ и __repr__:

from PyQt5.QtCore import QPointF

class Point(QPointF):
    def dist(self):
        return (self._p.x() * self._p.x() + self._p.y() * self._p.y()) ** 0.5

    def __add__(self, other):
        return self.__class__(super(self.__class__, self).__add__(other))

    def __mul__(self, other):
        return self.__class__(super(self.__class__, self).__mul__(other))

    def __repr__(self):
        return "{}({}, {})".format(self.__class__.__name__, self.x(), self.y())

if __name__ == '__main__':
    a = Point(1, 2)
    b = Point(2, 3)
    print(a, type(a))
    print(b, type(b))
    print(a + b, type(a + b))
    a += Point(10, 10)
    print(a, type(a))
    a += QPointF(10, 10)
    print(a, type(a))
    print(a*3, type(a*3))
    print("a: {}".format(a))
    l = [a, b]
    print(l)