There are some things over at divmod.org which I'm pretty sure should be part of Twisted.
We already imported Nevow's Deferred-capable templating in twisted.web.template. We should replace all HTML generation with twisted.web.template, if any still exists. It should also be generating HTML in a few more places; like, perhaps an admin UI to allow an admin to instantiate new resources, and I'm pretty sure we are avoiding at least a couple of useful bits of functionality on the basis of how incredibly nasty and difficult it is to generate some simple HTML without adding a mountain of new dependencies (which, of course, wouldn't support Deferreds).
The resource model from Nevow should be imported, with modifications. One of our oldest tickets explains some of the requirements for that resource model.
nevow.guard is basically just a more advanced version of twisted.web.guard, and should be imported, probably after the resource model upgrade.
Pretty much everything in Epsilon, I think, should be in twisted.python. Especially extime.Time, which would make the various things in Twisted that need to parse dates simpler and more consistent.