I know that's one of the reasons he's saying it, but that's not really everyone else' concern, too, and as I said security should come first. Firefox OS is coming to ARMv6 phones right now, so at the very least they shouldn't start with that in mind when establishing the minimum of performance for encryption.
There's the ARMv7 Cortex A7 chip for low-end now, and ARMv6 chips are terrible for performance anyway. They should not be used as a starting point for very low-end phones anymore.
ARMv6 is very similar in all regards to ARMv7 and there are very fast implementations available. Are you talking about ARMv5 perhaps, which has a terrible memory model making fast multitasking implementations with memory isolation very hard to implement? ARMv7 just adds some new instructions which are while usefu, does not give the performance benefits.
There's the ARMv7 Cortex A7 chip for low-end now, and ARMv6 chips are terrible for performance anyway. They should not be used as a starting point for very low-end phones anymore.