I love this idea. It makes `__slots__` easy and efficient to define! The current, explicit syntax is very tedious and verbose.
`__slots__ = ...` is a very clear syntax for saying "Include ALL annotated class-variables automatically".
It would relegate manual `__slots__ = { "a", "b" }` usage to when you want to define slots without annotating the variables, which pretty much nobody does.
So in effect, this new syntax would mean that everyone who wants slots in their classes will use the easy triple-dot syntax!
It would be a very nice language improvement.
(The `@dataclass` system itself still needs a way to allow "default variable values" (in the auto-generated `__init__`) if slots are used, though...)