It would be just a matter of time before someone starts making larger rams that are capable of doing the job better than the average ram, and even if that fails, the large players will end up owning enough RAM that makes everyone else's ram pretty useless, ASIC miners came as a natural result of people's desire to make more money more efficiently, it doesn't matter how you want to start the protocol, RAM, CPUs, GPUs or even light bulbs, the system will evolve and we would still end up with something like ASIC miners.