This has nothing to do with any proposed hard forks of Bitcoin.
The hard fork being referred to is internal to P2Pool, and has already happened.
P2Pool has something called a sharechain is parallel to Bitcoins blockchain, only using a 30 second block time rather than a 600 second block time. It is internally used for tracking mining progress in the pool, and ordering payouts. It has the same features as the Bitcoin one, in that it is completely in consensus between all the P2Pool nodes and has very specific rules for what is acceptable and what is not. Some rule altering is a hard fork, where previously invalid things become valid after the change.
The reason a hard fork needs to happen is that BIP66 enforcement will cause all subsequent version 2 blocks to be invalidated, anybody mining a version 2 block after this point in time will be throwing away money. P2Pool had to be internally hardforked to support version 3 blocks, or risk just burning all of the miners income on rejected blocks. This Bitcoin soft fork will happen very shortly, when the average version of the last 1000 blocks is 2.95, which is why P2Pool had to make such a drastic change in such a short period of time.
P2Pool is unlike all other centralized pools in its operation and management. Other pools simply updated their Bitcoin nodes to the latest version of the software and anyone mining with them accepted the soft fork by proxy.
I have read on here that hardforks are a point where the pool with the biggest stick gets to decide which course the blockchain will take.
This is not correct. A hard fork is controlled by the users of the network, not the miners. The miners must mine blocks which the network views as acceptable, if they don't the nodes in the network will simply reject their (to the rules they have) invalid block and ban the peer that sent it to them.
Has the hardfork only just begun?
There is no accepted proposal for a Bitcoin hard fork.