A topic after my own heart. Even some Elinor Ostrom references 
I see.
Simply put, I think you need an actual legal entity here called the “ActivityPub Foundation”. How that entity is run and governed is another question. But if you have an actual thing with the name of the thing (i.e. “ActivityPub”), folks checking their boxes for a grant application are much more likely to look favourably on it.
I totally get the impulse to sort out the “how we work together” without any formal structure. But it does make things like grant applications harder. And, relatedly, can result in a lot of unacknowledged labour on the part of folks in the role of @how (and others).
This is why with Pavilion (a workers cooperative), I established it as a very simple UK corporation, and, post-brexit, Estonian corporation (easiest EU jurisdiction to register in), and then worked out the “how we work together” piece afterwards. Having that simple setup meant that we could easily work with clients and apply for grant applications while we were still figuring out the very difficult “how we work together” piece of the collective effort (we’re still figuring out pieces of it). This (i.e. the ActivityPub community) is a different kind of effort from Pavilion, but I think a similar kind of thing applies mutatis mutandis.
It does mean that you have to put some trust in whoever’s associated with the simple entity you set up, but I think that’s actually a much easier issue to manage (in this kind of situation) than the converse, namely burnout along with unacknowledged labour.
To be clear I don’t think the person with their name on the thing should be me, I have too many conflicts of interest, that’s not what I’m angling for here. But there should be an entity with “ActivityPub” in the name if you want to increase the chances of grants like this.