Not implausible, which roughly translates into highly improbable. The cost and time-frame to implement would make it a pointless exercise, they would only use the processors themselves and volumes would not be anywhere near sufficient to get any economies of scale. Apple have so far only just completed a semi custom ARM design which is a million miles from a fully custom processor. Do these people have any appreciation of how much effort and cost is involved in doing this from scratch. Surely if they did they would realise how pointless it would be given the current direction Intel is taking with its offerings. By 2017 it is likely Intel will have similar performing mobile processors to ARM, the only thing currently lacking would be the ability for 3rd parties to integrate Intel designs into SOC designs and is currently a big advantage for ARM designs, if Intel can overcome this they will be a real across the board option by then. ARM is currently lacking any high performance processor designs for power laptop and desktop plus you have to then transition all software to RISC if you go this route which is another huge undertaking. You would be in the realm of Rosetta again which was hugely painful last time but at least had the huge benefit of getting Apple onto superior x86 processors and able to run windows software using virtual machines or boot camp.