We already have cheap comodity ARM chips, it's called the Raspberry PI . It didn't make much of a dent in the X86 market. It's a niche of it's own in the consumer tinkerer and industrial embedded devices, but desktop computing is a tough market to crack, as explained by Linus Torvalds.
Having (non-Apple) ARM assault the X86 ecosystem will take a lot of out of the box thinking and, most importantly, cooperation for standardization amongst the HW vendors for open standards, which is exactly what Nvidia doesn't like to do, as they always prefer the locked down ecosystem approach, contrary to the openness that lead the comodization and popularity of the IBM PC clones.
Having (non-Apple) ARM assault the X86 ecosystem will take a lot of out of the box thinking and, most importantly, cooperation for standardization amongst the HW vendors for open standards, which is exactly what Nvidia doesn't like to do, as they always prefer the locked down ecosystem approach, contrary to the openness that lead the comodization and popularity of the IBM PC clones.