At some point, we need a modern redesign alternative to pprint. It could have its own __pprint__ method to communicate how it wants to be pretty printed.
Until then, I think the existing pprint module should only grow custom support for classes that have a mostly consistent structure and usage pattern. SimpleNamespace, for example, made sense for a custom pprint handler because it is so dict like and is almost never customized.
IMO, dataclasses are a bridge too far. Having pprint() guess what a dataclass intends is not far from try to guess what an arbitrary class intends. This is skating on thin ice.