just wanted to make sure i understand. if this makes it into the client, then those mining on p2pool can use the classic bitcoin client. if it doesn't make it in, they either need to use the bitcoin client patched with this or they can mine without this path but if that node happens to solve the block, it will be absent any transactions?
specifically, what i am wondering is lets say half the p2pool miners are running with this and half aren't. do they work together or are there forking p2pool sharechains?
The p2pool sharechain won't fork, each share has its own set of transactions and each node has freedom to include whichever it wants.