I'm really excited by this idea. Thank you, Robin!
I imagine the way forward is exactly what Robin suggests in her answer below: user accounts for projects.
If a project has an account, it can be put on Trusted Lists, and if appropriate set as the manager of profiles. This gives it a Watchlist. The Watchlist would essentially be a list of all profiles covered by the project, and the Watchlist Activity Feed would be a feed for all the activity in them.
One issue with this approach is that we have a rule against accounts being set up for anything other than a person. Person profiles on our tree and member accounts are inseparable on WikiTree.
But I think we just need to establish when and how it's acceptable for something other than a person to have an account. We can still have the general rule against it, and be careful about how we do them. (This is on the top of my mind today because of something completely different: edit bots, i.e. programs that automatically make changes to profiles on a member's behalf. Much more to come on this later/separately.)
Maybe we can start an account for one project and see how this would work? The first question to address would be the e-mail address associated with it. It needs to be a new address, not one already associated with an account. We could set up an @wikitree.com address for these, e.g. euroaristo@wikitree.com. It would have to be an "alias" for info@wikitree.com and mail would come to the team.
Chris