I think that the scan-as-you-shop style systems are definitely the next realistic step for grocery stores. I really like using them, as they allow me to put stuff directly into my bags as I go. I think a further improvement on a system like that would be to use the cheap RFID tech (UHF EPC) so that when you walk through the anti-theft barriers, the system knows exactly what you got, and then there's no need to scan a…
Unfortunately I doubt you'll ever see this happen.
Sure, it's supposedly possible to buy an RFID chip for 1p - but you can buy a can of beans for 23p so that 1p is probably their entire profit margin.
I've also worked with a variety of RFID readers; none of them can provide reliable reading, even in favourable conditions.