A note for when we are ready to finalize the copy for this: I think we should think of a way to indicate that adding an email is not just for account recovery -- it's also the way to find out when important/relevant things happen on the wiki. One of the reasons the Growth team is addressing this idea is because we believe that when newcomers find out what's going on in the wiki, they are more likely to come back and keep editing. We should be upfront about that to the user.

Should we add something about Privacy, which is a WIkimedia core value?

We value and protect your privacy. Your email address will only be used for account recovery and receiveing some notifications you choose.

An alternative with less friction is to prompt people to set (or confirm) their email address when they reach a certain level of actitity (e.g. 5 edits). That way you avoid holding up the vast majority of users who register but never make an edit. See T58028: Show Echo web notification (asking users to consider providing an email) to users who don't have an e-mail address associated with their account.

Copying this from the other task so it doesn't get lost:

In T159837#4703682, @Anomie wrote:

In T159837#4702907, TheDJ wrote:

Nirzar proposed to make some further changes

Keep in mind that whatever changes get made have to work with the action API's action=createaccount too, and for people without JavaScript enabled, and on third-party wikis that have different authentication providers installed. In particular, having a button (rather than a checkbox) inside the popup thing seems very unlikely to be workable.

To clarify: it's ok from this perspective if those other cases just don't get the prompt when proceeding with the creation. It's not ok if they can't create the account because the button isn't available. It's also not ok if people wanting to click a "Login with Google" button get tricked into clicking a button that does something different.

Our team has decided that we will not be working on this project during Q4. Moving it to the next fiscal year.