Cool ideas.
Very soon, next week I hope, we'll finally get Wagn 1.13 out the door, which will mean that all account handling is done in cards. That, in turn, means all account handling is exposed to the mods API, so it will be much easier to add mods for account-related stuff (including signups, signins, etc).
I definitely see that there's a need for more options here.
I'll be writing more about the changes coming as we lead up to the release. Would love it if folks were inspired to try to write some mods to tackle new anti-spam solutions!
-e