We don’t have any planned support for “inheritance” of structs, but we should be able to do what you’re talking about with containment like that. It sounds like you’re looking for better support for variadic types?
The major challenge we have right now is that we don’t support nice variadic unpacking - there are a variety of workarounds, but I agree it is not very beautiful. For example, you can see how various types build on top of heterogenous varadic types in the standard library: Tuple is the canonical example, and the VariadicPack type in the standard library is what is used to implement the syntax.