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.
What you are not taking account of is transaction size. Bitpay (for example) allows the vendor to choose the confirmation level (risk), and they usually do it based on the transaction size. So a Starbucks isn't going to wait for confirmation or 1 at most, but your local BMW dealer will probably say 'come back in an hour'.
The key here is that retailers have absolutely nothing to lose, and much to gain by accepting BTC, it's just going to take time for the Bitpays of this world to grow enough to make the difference we are all waiting for.
On a slightly more optimistic note, the delays and problems as your correctly point out are all caused by having to deal with third parties. Thats only going to happen whilst we still need to convert to pesky fiat. Consider what happens when we reach tipping point, and vendors start holding/using BTC rather than fiat!