Re: 50 billion IoT devices
Typical ARM pricing is around US$5-$15/SoC per 1000
Typical Atom pricing was around $25-30/SoC per 1000 (possibly even lower with rebates/subsidies to get their chips into products)
Typical x86 pricing is US50-$2000/CPU per 1000
These are rumoured prices manufacturers were paying versus RRP. Price isn't everything, but you have to have sufficient yields and sales to cover your R&D/manufacturing/sales/C-level bonuses/dividends.
ARM has the advantage of being cheaper and easier to make, but Atoms weren't where the money was for Intel. There might have been a window where Atom could have been brilliant and ARM failed to increase performance that gave Intel the opportunity to compete in mobile devices, but it didn't happen.
As ARM move forward, they will need to increase their complexity to incorporate a longer pipeline and cache which will drive an increase in SoC size and therefore cost per unit. ARM manufacturers can put pressure on Intel and Intel's margins will continue to fall, but Atom being dropped isn't the death of Intel and they still have a 2+ year lead in process technology.
At the risk of insulting them, Intel may not have the best technical CPUs on the planet, but they have been the best CPU manufacturer (sometimes at the cost of performance/technical excellence to allow higher yields) for decades.