I haven't edited or updated the comment at all since I originally wrote it, but the offer to reach out to me is still open!
I don't know of any single "Cause Y" that can easily absorb hundreds of people with a standardized training protocol, but I suspect that there are dozens of small projects that would be worth trying and wouldn't take much individual research to prepare for.
For example, EA Giving Tuesday was an independent project run by a couple of people who noticed an opportunity and took it, in turn giving hundreds of other people a chance to boost their own impact. (The EA Project for Awesome example you listed here is similar.)
There are also various lists of project and research ideas online. No one person will be suitable for all of these, and perhaps no one training program could reliably prepare anyone for a particular project, but any given person may be able to find at least one project idea that "fits", even if their role is market sizing or design or copyediting rather than direct research.
There's also lots of volunteer work available. EA Global and Rethink Charity use quite a few volunteers, for example, and plenty of other EA projects would benefit from more eyes/hands/minds:
- If you speak another language, you can translate something important for a new audience.
- If you're a good editor, you can help someone with an unpolished paper on Effective Altruism Editing and Review.
- If you have design skills, you can ask an author if they'd like you to create an infographic based on a paper or Forum post. Owen Shen does something similar for EA San Diego, creating flyers and graphics for upcoming events.
- There's an EA Volunteering Facebook group with lots of other opportunities and ideas.
While we don't have a single Task Y, there are a lot of ways to get involved, many of which could help you qualify for an EA Grant or find a job down the line. Anyone who reads this and wants ideas beyond what I've listed here is welcome to reach out to me.