Something that's on many of our wishlists is support for variadic generics. Here's a first draft of a PEP detailing how they might work.
https://docs.google.com/document/d/1oXWyAtnv0-pbyJud8H5wkpIk8aajbkX-leJ8JXsE... (Attached is also an HTML render of the RST for easier reading.)
This is an early draft so there are likely many things we're still missing. Please do take a look and give us your feedback (in the doc directly or by email, whichever is easiest for you).