Hi @Jc86035 -- thanks for posting here and for caring about new editor retention. The Audiences department here at the foundation has thought a lot about this topic over the last year, and we actually have several things ongoing that address it. You're right that the engagement of new editors has been decreasing or being stagnant since about 2007. This paper discusses exactly how and why.
One of the things we noticed, however, is that a lot of people attempt editing, but very few stick around and keep editing. Therefore, we have thought less about recruiting new editors, and more about retaining the ones who do show up. For instance, about 2,000 new users create accounts in Korean Wikipedia every month, but only about 160 of those will come back to edit more than once. That's what our team is focused on: new editor retention (specifically in mid-size Wikipedias, who have challenges with "getting over the hump" of having enough content to be reliable sources of knowledge in their societies). You referenced that concept of a "funnel" in your proposal (e.g. maybe people don't know they can edit), and this paper talks about that specifically. And the foundation's research on new editors also digs into retention.
There are also a couple other teams working on retention of editors, such as the three teams working on mobile editing. That became a priority because we learned that newer generations and cultures coming online would much prefer to edit on mobile than desktop, and therefore having that option available would help retain new editors.
So with respect to the ideas you listed, I think the first two are "higher up in the funnel" than we are focused, because they are about informing people that editing is possible. (The New Readers team, however, did advertising last year in a couple countries to inform people that Wikipedia even exists). But the third idea is actually one that our team is thinking of prioritizing. When we discussed potential retention ideas with the broader community a few months ago, the idea of contacting new users to bring them back is one that we discussed positively. We ultimately decided not to work on it first, but it is on our short list for the future. I encourage you to go ahead and add things to that discussion page if you have thoughts on that (or any other idea).
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