Metaculus has currently got over 1000 open forecasting questions, many of which are longtermist or EA focused.
These include several EA-focused categories, e.g. EA survey 2025, an Alt-Protein Tournament, Animal Welfare, the "Ragnorak" global catastrophic risks series, and other questions on the distant future.
I am volunteering at Rethink Priorities doing forecasting research, and am looking to see if there are EA related questions with long time horizons (>5 years) people are interested in seeing predictions on, and if there are I am willing to put some time into operationalising them and submitting them to Metaculus.
I think this would be both directly useful for those who have these questions and others who find them interesting, and also useful for expanding the database of such questions we have for the purpose of improving long term forecasting.

This question is part of a project of Rethink Priorities.
It was written by Charles Dillon, a volunteer for Rethink Priorities. Thanks to Linch Zhang for advising on the question. If you like our work, please consider subscribing to our newsletter. You can see all our work to date here.
This sounds like a cool idea, thanks for doing it!
One place where you could find a bunch of ideas is my Database of existential risk estimates (context here). It could be interesting to put very similar questions/statements on Metaculus and see how their forecasts differ from the estimates given by these individuals/papers (most of whom don't have any known forecasting track record). It could also be interesting to put on Metaculus:
On the other hand, forecasting existential risks (or similar things) introduces other challenges aside from being (usually) long-range. So this might not be the ideal approach for your specific goals - not sure.
(This is a somewhat lazy response, since I'm just pointing in a direction rather than giving specifics, but maybe it could still be helpful.)