There is currently no instances for Ratio data type that can give us random values

Edit: - It looks like we are in a agreement that Uniform and UniformRange instances are not possible for Ratio. Question then is, should we add a Random instance, which doesn't really promise uniformity?

I can see a reasonable Uniform instance for integral types, which excludes the zero denominator:

instance (Integral a, Uniform a) => Uniform (Ratio a) where
  uniformM g = do
    n <- uniformM g
    let notZero = do
          d <- uniformM g
          if d == 0 then notZero else pure d
    (n %) <$> notZero

An efficient version for UniformRange needs some thought.

Note that neither Uniform, nor UniformRange would be able to generate Rational. This means that we can attempt and cook up such instance for Random