We lose out on some future flexibility to add new methods, which
might amount to nothing, or might be a big deal.
Wouldn't we just introduce the type then once we needed it? It would
be awkward, but would it be impossible or inadvisable?
That would not be binary-compatible.
Let's say we had
record Foo(int x) {}
which was translated without a supertype. Now we later try to add in
the supertype, say with a `.toJson()` method, but don't recompile Foo.
Then:
Record r = (Record) aFoo;
String s = r.toJson();
compiles, but throws some form of IncompatibleClassChangeError, since a
Foo does not extend Record at runtime.
