Need feedback, ideas and devs for rethinking signups!

I have been thinking a lot going back a couple years about re-imagining the registration and login/logout process for WP, especially MultiSite. It eventually leads into other areas like welcome messages for new users and management of sites as well.

I have an overview here:

A gist of immediate plans here:

Some of this was discussed in dev chat just today and some will be addressed as ticket scrubs for 3.7, some will hopefully be aimed at 3.8 or later, depending on progress.

I have an experimental plugin as a proof of concept:

The goal is simple urls like /signup, /signin and /signout. Then a page setup that works like the templating system for themes so themes and plugins can easily customize and override any part of it.

But it needs feedback, ideas and if anyone is up for it, fellow coders to work on it.