PEP 484 will drop its provisional status at some point. I hope this will happen in time for 3.6.
I propose to create a milestone to estimate how much work should be done before this happens.
Here are some issues that I propose to add to this milestone:

Big things:

• The notorious Kill __subclasscheck__ #136 (and Bare Union, Callable and Tuple should not be classes #133, typing.MutableMapping not a drop-in replacement for collections.abc.MutableMapping #203 that depend on it). This bug requires substantial changes to typing.py. However, it does not require PEP change and there is already a PR Fix generics inheritance and drop __subclasscheck__ #207 so that probably it will not take too much time.
• Protocols (a.k.a. structural subtyping) #11 (Protocols) It looks like a very convenient tool, and it is suitable for Python's duck-typing. There is already a concrete proposal by @JukkaL Protocols (a.k.a. structural subtyping) #11 (comment) that was positively accepted at python-ideas.

Smaller things:

• Introduce an Intersection #213 (Intersection) This will be very easy to implement in typing.py. It will work nicely with protocols. Also I could speculate that mypy implementation will not be too difficult (it should be similar to Union).
• Make Callable more flexible #239 and Proposal: Generalize Callable to be able to specify argument names and kinds #264 (flexible Callable) This feature has been requested several times, and it is really easy to implement in typing.py, there are some detail to discuss.
• Allow subclassing without supertyping #241 and Declaring classes as pure mixins #246 (Implementation) It seems that an agreement on this is quite close.
• Decide how to handle str/unicode #208 how to handle str/unicode.
• A way to spell "SelfType", the type of self #271 SelfType and type annotations of classmethods? I am not sure about this one.

I could volunteer to take care about all of the above except #11 (it probably will be better done by Jukka) and SelfType. By "take care" I mean make PRs to PEPs and typing.py. However, I do not exclude also working on some of these in mypy if necessary. I think it is not necessary for mypy to support all the features at the point when PEP 484 drops provisional status, they could be implemented later.