This is an incomplete list of next steps to build proper stubs from PyO3 codebases:

• introspect all class methods (including adding a test for all magic methods) (partial: Refine some magic methods introspection #5273)
• introspect classes associated constants (const) Introspect class associated constants #5272
• introspect modules associated constants (const) add declarative module level constants export #5096
• introspect simple enums built by #[pyclass]
• introspect complex enums built by #[pyclass]
• introspect exceptions built by create_exception!
• introspect class inheritance (#[pyclass(extends=)]) Introspection: Basic pyclass(extends) support #5331
• @typing.final decorator on class that cannot be subclasses (without #[pyclass(subclass)])
• introspect auto-generated magic methods (#[pyclass(eq, eq_int, ord, hash, str)]) Generate introspection for #[pyclass(eq, eq_int, ord, hash, str)] #5338
• introspect fields getter and setter (#[pyo3(get, set)], #[pyclass(get_all, set_all)]) Introspection: support #[pyo3(get, set)] and #[pyclass(get_all, set_all)] #5370
• implement return type annotation Introspection: implement output type #5208
• fill PYTHON_TYPE constant on all implementations of the relevant traits (FromPyObject and IntoPyObject)
• fill INPUT_TYPE in #[derive(FromPyObject)] Basic introspection of #[derive(FromPyObject)] #5339
• fill OUTPUT_TYPE in #[derive(IntoPyObject)] Basic introspection of #[derive(IntoPyObject)] #5365
• figure out how to emit #[classattr] in the stubs
• support cross-modules types (class defined in module A and used in module B as an input/output type)
• add doc strings to the generated stubs
• proper test coverage
• proper formatting of stubs (not a blocker)
• integration into maturin
• proper type stubs for containers (list[T] instead of list). Blocked by generic_const_exprs being unstable
• allow to set custom type annotations (both inputs and output) Introspection: allows to override annotations in signature #5241
• allow to set custom stubs for eg. protocols
• add _typeshed.Incomplete to relevant places (modules with a #[pymodule_init] function...) (doc) Introspection: properly tag modules as incomplete when needed #5207
• choose between _typeshed.Incomplete and typing.Any in type annotations
• make sure to properly gate introspection element with cfg macros
• provide a way to set @overloads
• Support WASM files in pyo3-introspection
• Allow custom type annotations without strings (example: #[pyo3(signature = (arg: list[int]) -> list[int])])

Reference on stubs file