The problem with all statements regarding programming languages is that they rarely have empirical evidence to back them up. Do you have any data showing that generics will lead to a cleaner language? I have seen a study or two that tried to measure productivity, bug counts, etc with regards to generics and what it showed was that writing code using a library that is built with generics was ever so slightly faster. However, it showed that creating or editing a library that used generics took 10x longer.

It seems that you can't really make the claim that adding generics leads to a "much cleaner language".