> the node for Desktop ( High Performance ) will be different to Phone / Tablet ( Low Power )
The iPhone CPUs are already competitive with Intel chips. They've got incredible single-core performance, great memory bandwidth, and solid 64-bit and SIMD support. What specific feature of a "high performance" node would they require that they aren't using for iPhones now? They've been pushing the limits on allegedly "mobile"-oriented architectures for years.
Every time this comes up, I hear from the naysayers "Yes, Apple is great at mobile, but desktop is a different game", but then also "Apple's mobile chips are faster than many Intel desktop chips". The skeptics sound awfully similar to those who said "Apple is great at iPods but smartphones are a completely different game".
> The cost of designing and testing a 5nm chips is roughly a billion.
AFAICT, nobody in the world has a production 5nm chip yet. How can you put a price on something that nobody has successfully produced yet?
If I were Apple and I were confident that just throwing $1B at it would solve all the engineering problems, I would absolutely do it. $40 per Mac for the best CPU (and independence from Intel) sounds like a steal.