This particular snippet that you quote talks about dynamic languages that want to interop with the rest of the CLR language ecosystem. Because CLR provides a strong static type system that has reified generics, it means that dynamic languages have to devise ways to interop with that system. For example, if you're in IronPython, and you want to create a list that is strongly typed from C# perspective, you have to do something like this:
from System.Collections.Generic import List
lst = List[str]()
lst.Add(123)
obj.DoSomething(lst)
However, this is only an interop problem. A dynamic language targeting the CLR that does not care to interop with C# does not have to do anything special. And none of this has anything to do with the GC - that operates on a level far lower than anything to do with generics.
(I would also claim that the quoted snippet vastly overstates the problem, while also misrepresenting it - it has all to do with static/dynamic type system mismatch, and practically nothing with reification. In practice, if you want to interop between C# and Python, you'd just use "dynamic" in C#, and access native Python collections directly - that's exactly the scenario it's intended for. The only time you'd need to muck around with generics from the Python end is when you're calling into a library written with C# - but that's just FFI, no different in principle than having to specify types when you're using ctypes to invoke into C.)
(I would also claim that the quoted snippet vastly overstates the problem, while also misrepresenting it - it has all to do with static/dynamic type system mismatch, and practically nothing with reification. In practice, if you want to interop between C# and Python, you'd just use "dynamic" in C#, and access native Python collections directly - that's exactly the scenario it's intended for. The only time you'd need to muck around with generics from the Python end is when you're calling into a library written with C# - but that's just FFI, no different in principle than having to specify types when you're using ctypes to invoke into C.)