This whole malleability fiasco has shown once again that zero confirmation transactions can not be trusted.
since its not practical waiting for 10 minutes for a payment to clear when buying coffee it seems to me that bitcoin will never go mainstream in physical shops.
any solution involving a third party to clear payments defeats the whole purpose of bitcoin.
any third party will effectively turn into a bank along with all the classical fractional reserve practices we have today.
In my view, one of two things will happen. Either Bitcoin will become a viable alternative to gold as a store of value, or a service will be built on top of Bitcoin that will allow it to facilitate instantaneous transactions. This would be something like Coinbase or a bitcoin bank, with apps on phones which allow this to happen.
Alternatively, Bitcoin will remain a store of value, but another currency like NXT will become the standard for rapid retail transactions.