Broadwell ULX is just 4.5W TDP, and will allow fanless x86 laptop. It is however still sometime away, so I don't see this rumored update happening "soon".
Interesting but the rumour says the update is coming soon. If they switch to ARM processor they could also reduce the cost of components and reduce the retail price. It would also open up the MB to whole lot more apps. Seems a win win to me. If you want the power of an Intel processor you would probably go for the MBP rather than the MBA anyway.