This article highlights very well why designing a programming language without generics is a mistake. Adding it after the fact is not trivial, especially if you have high standards wrt simplicity and non-redundancy.
It seems crazy to me that language designers of modern statically typed languages wouldn't go for the state-of-the-art. I see the comments about simpilicty, but generics makes [working with abstract types] simpler (in my humble opinion, of course).
The task that lead to my decision to quit was to write a data serialization systems for datastructure that I didn't know in which version of junk they were expressed, by interfacing with the broken standard library. The serialization system was to replace another serialization system that somehow didn't quite work. No wonder, it was broken code, and I couldn't see a way to write non-broken code to solve an unsolveable problem.
What's nice about Delphi is that the compiler is quick and it has a beginner-friendly IDE with a visual GUI creator (no selling point for me). That's about it, AFAICT.
interface{} is already promoted to heap, they are pointers, all you need is to swap interface with type parameter and add a couple of hundreds lines of code to the type checker. The theory is all in the books and there are dozens of compilers implementing it in practice.