Community efforts include more than just the efforts of the official teams.
Aside: I'm going to be use quotes (") in this post to differentiate between people belonging to teams ("team") and those who aren't ("community") - in practice team members are part of the community, and it's more about differentiating those keeping very close tabs on wide part of rust development/RFCs vs those who are less acquainted with what's going on.
When I hear "focus community effort" I don't think of the teams, I think of "community" attention - involvement in RFCs from people not on the official rust teams: reading the huge comment threads, adding comments, critiques and feedback, trying out the unstable features, etc.
The organic attention of the "community" often does not line up with the attention of the "teams". Consider RFC's written and postponed, or RFCs that garner lots of comments without team attention. I think in part the drift between "community" and "team" focus has gradually grown as the community has gotten bigger. It's easier to follow what's going on when less is going on.
I think negative RFCs would be useful for "community" involvement - I think that with negative RFCs/space there would be a fair number of RFCs that would be unwritten, instead of written and then postponed. Knowing something won't get much attention beforehand is pretty valuable. And it's hard from a community perspective to know what that is.
I think negative RFCs / negative space is only one approach to this though, so don't take this as endorsement.
I do think in these discussions it's useful to keep in mind that that what helps "team" members might actually inconvenience "community" members, and vice-versa.
TL;DR - "team" members and "community" members interact differently - I think the negative space RFC stuff was for the benefit of "team" members, not "community" members. I think it's important to consider both though.
Personally, I'd go for more tooling making it easier for team members to mark where their attention is, and aggregating it into an index / portal that makes it easier for "community" members to see where attention is allocated.
Also, I'd gladly accept a slower pace of rust language development for better rust community involvement.