Discussing an option with the community to test replacing registration CAPTCHAs with an email requirement makes sense to me. I would support a small, carefully designed test. If someone is motivated to create a Wikimedia account and they don't want to register an email, they can be given the option to have someone help them to set up an account via IRC, Facebook, or other communications methods.
I'd very much like to hear input from stewards who deal with cross-wiki spambots, so I suggest that the designers of the test consult with one or more stewards during the test design process.
Pine