If a PPS operator wants to eliminate block withholding risk, he can lobby for my oblivious shares proposal.
The only remaining question for me is then:
Is block withholding (which essentially removes the hash rate of the withholder) the only risk left in a "pure" PPS pool?
It should be detectable by the way, if you are willing to invest a few coins for that (or cheat a tiny bit on your miners) - as soon as someone has solved a valid block you send out that getwork manually to all of your miners connected at that time and kickban everyone that doesn't send a reply. If they send a reply back, you can either choose to pay them for their honesty or just treat this share as stale and not pay it.
All in all miners loose ~3000 Satoshis on that share but you gain a lot more security without having to beg all mining client developers to implement oblivious shares (as far as I understood it, it also requires changes on the miner's side).
On the other hand, with the current pool model you won't be competitive anyways, there are already enough other pools out there - so you anyways need to be more innovative.
As an example:
A miner can also deployed via BOINC (which is also able to handle requesting work and managing credits etc.) and some exchanges can be scripted to automatically change money to USD/EUR... combine this, put in a reasonable fee and get some profit going on. You wouldn't even need to handle payouts, as both MtGox allow you to move BTC (TH) or BTC/USD (MTG) between accounts, you just move the mined money to their account (and if they hand you an API key, automatically bot-trade that money for fiat, if desired) and let them handle it from there. You might even be able to get lower fees + referral income (at least on TH) and all of that can be done _right now_ already if you combine the right pieces.