Is this a reference to some specific, better, technique or an optimistic belief that such a thing could be built if only ..?

Code generators are used because run-time introspection tends to be slow(er) and because debugging code generated at runtime is harder and because IDEs don't know how to deal with code generated at runtime. But there no reason why this should be so. No good reason to have a hard boundary between compiletime and runtime either. These are just historical artifacts.