For some more background, when we proposed something like that to Chris
Steipp he was pretty iffy about it, and he's not wrong. At other sites
that
don't have a CAPTCHA on signup (like Facebook,
Quora, others) they avoid a
spam problem in part because they require an email address and
confirmation. For some irrational reason, even in the era of throwaway
email accounts from web services, not requiring email is some kind of
sacred cow among Wikimedians, even if it would make it an easy choice to
throw away our wretched CAPTCHA.
Because spam bots can't answer email?
If we want to avoid spam bots signing up, there is
going to be a hit in
ease of use somewhere. Our network of sites is just too large to avoid
being a target. It's just a matter of testing to see how much we can
reduce
that hit, and which method might be less easy.
There is really no evidence that the current hit in ease of use has any
affect on warding off spam bots.
--bawolff