Two comments:

1) So far this proposal doesn't explicitly describe how to pay the nodes who construct a block that contains all the transactions minus the coinbase, for their service. If it should be some sort of a subscription service where the PoW miner pays in advance, then this adds to the overhead because the miner has to identify himself when requesting a new block, and there's room for abuse/freeloading i.e. one miner pays and then shares his account (login/password) with other miners, or shares the constructed block (minus the coinbase) with other miners. Another option is that it'd be some kind of an honor system, where miners donate some portion of their profits to the nodes who provide this service, but I'm not sure if that'd be sustainable.

2) In an old thread the issue of performance was discussed, slush's reply (link) is rather pessimistic. He considers the straightforward setting where the miner submits the entire block to the pool, unlike your followup post about quizzing or using SNARK/SCIP as an improvement. Though unlike the old thread, with multi-PPS there's the added complexity of interacting with separate nodes that construct blocks for the miners, and this should also be taken into account since the miner might request several such blocks during the average 10 minutes interval, as new transactions are being broadcasted over the network. I think that BIP0022 (which probably isn't being used by anyone yet?) was inspired in part by that old thread, so I'm not sure what should be the current assessment regarding the severity of the performance issues.