It's less about the immediate raw effort and more about the ripple effect such a thing would have for both past, present, and future writing. TiTS is already critically overloaded with a lot of appearance features, aesthetic customization, and player character traits that go almost completely unsupported by authors, and adding another one, let alone such major one in the form of multiple arms (because it would be quite major), would be like tossing more fuel onto a fire that's already burned down an entire city.
We can barely get meaningful support for multiple legs in the form of taurs (barring Wsan, who couldn't stop the madness even if he wanted to), which are much less complicated than arms would be... >_>