cc @Niharika @Tchanders I wanted to put it up for discussion before we committed. I've chatted with both of you off-band about it and I think @Tchanders thought it would live in core, @Niharika was neutral, and I was very biased toward making it an extension.

We should decide by EOW if possible.

Additional consideration, if it helps - I was talking to Sherry the other day about this and she suggested this feature could have broader applications in the future. For example we could have this workflow apply to anyone who is blocked from editing if they are logged out but can edit if they log in. This is a rather frequent scenario for users who live in cities where large IP swaths are blocked.
To clarify, this is not part of our work right now. This may be something our team or another team may want to build in the future.

• Which wikis are blocking IP editing, and how are they doing it?

Portuguese Wikipedia is the only wiki blocking IP edits right now. (Farsi did in the past, but not any more.)

What happens when you try to edit logged out on ptwiki?

Desktop:

1. Click on the edit button on an article page, logged out
2. You are redirected to Special:UserLogin, with a banner explaining that the community has decided that editors need to be registered users

Mobile:

1. Click on the edit icon on an article page, logged out
2. An overlay appears with a message that you are welcome to edit as a logged in user, with buttons leading to Special:Login and Special:CreateAccount

How does this happen?

On desktop, the edit link is redirected to Special:Login via the community JavaScript: https://pt.wikipedia.org/wiki/MediaWiki:Common.js#L-112

On mobile, the normal edit warning message about exposing your IP address is overridden: https://pt.wikipedia.org/wiki/MediaWiki:Mobile-frontend-editor-anonwarning, and the edit button is hidden by setting the CSS rule display: none.

In T319501#8327120, @Niharika wrote:

Additional consideration, if it helps - I was talking to Sherry the other day about this and she suggested this feature could have broader applications in the future. For example we could have this workflow apply to anyone who is blocked from editing if they are logged out but can edit if they log in. This is a rather frequent scenario for users who live in cities where large IP swaths are blocked.
To clarify, this is not part of our work right now. This may be something our team or another team may want to build in the future.

Thanks for the additional context.

Depending on the requirements for now, there would be two quite different technical approaches:

• If we just want to add the new workflow to ptwiki, then we would need to implement it within their community JS/CSS, or at least modify that community code to allow what we implement to work. We'd need some help working with the community on this, and understanding what we are and aren't allowed to change. Our work would only be useful for ptwiki, as it would work with the specific way they have chosen to disable IP editing. I note that this would also be an example of the Foundation investing resources in this community's decision to turn off IP editing. Presumably AHT would need help from community experts to negotiate and communicate this decision?
• If we want to add the new workflow for all logged out users who can't edit, we should implement that in core, as it would be a core feature that helps everyone in this situation. ptwiki could choose whether to change their community-written code to use our workflow, or not. Our work would be useful in many existing situations, and would remain useful if the ability to turn off IP editing is ever added to MediaWiki core.