Well, Perl 6's type system has difficulties
with respect to numeric types, because they don't form a nice hierarchy. Luckily we have roles, and thus can have a type of all (scalar) numeric types without pressing them into a hierarchy.
Implementing the numeric types correctly is a bit tricky, but the fact remains that the user (aka Perl 6 programmer) can simply add (or override) operators for each pair of types. If one of them is always a user-defined one you can guarantee no clashes with existing semantics.
So I don't see how Perl 6 isn't a solution wrt to adding new numeric types to the language - would you care to elaborate?