I think IDLs are an important point among many others (I attempted to list some above). I think we might be missing substantial improvements if we'd just say "oh so we're back to a static IDL description, all old is new again".
And even within IDLs, we've made major progress. Compare the mess of SOAP's data type system, various attempts at inheritance and polymorphism in SOAP and CORBA, pointers in CORBA etc.
Apparently DCE IDL now comes in proto files.
What newcomers did not bother to understand is why we were using those formats in first place.
Rest assured, maybe in 20 years we will be introducing this cool RPC protocol, based on YAML on something. Thankfully by then I should be retired.