3. Vertical scalability that reduces variance for all miners.
This is where the real challenges lie.
For p2pool to support large mining operations, and still be able to attract medium, small, and micro miners we need completely new share difficulty and payout structures.
The first step here has nothing to do with code, some completely new concepts need to be developed and generally accepted by p2pool miners. Once we have those concepts down, and can demonstrate them to be technically possible, we can seek out devs with the chops to pull it off.
P2Pool in it's current form is just not scalable. As others have pointed out the current sharechain model only becomes worse as more hashrate is added.
Perhaps a model where we have "super nodes" that split out smaller sharechains could be considered. I also think the concept of pseudo shares in-between real shares should be eliminated or modified so that work is not wasted.