But if you look at the software ecosystem Apple is slowly but surely building, and at the patents, there are good chances that the first desktop-oriented ML accelerator they will ship might surprise a whole bunch of people.
...pretty much agree with everything you said - my only question is, will there actually be a market for
desktop ML?
The two natural homes for ML are probably (a)
in the cloud (or private data centre) because that's where all the training data lives, and because it often makes more business sense to rent computing power on demand from the cloud and (b) mobile and embedded devices because that's where the
applications of ML that
can't rely on fast web access are (biometrics, photography etc. in phones, cars, smart devices...). You're not gonna want to carry a Mac Pro on your back to use the new AR goggles.
Both of those are areas where the power consumption & heat vs. performance considerations of Apple Silicon are an advantage. The "traditional" MP is not great as a high-density computing device, and it fits into the niche where the power consumption of the CPU is probably the least important (no batteries, plenty of space for cooling & you're not going to be stuffing hundreds of them into a data centre).
The current Mac Pro is very specifically designed as a standalone, super-powerful (by Mac standards) personal desktop workstation - and, squeezed between the cloud on the one hand and increasingly "good enough" mobile and SFF systems... well, with all due respect to the people who
actually do need such a system
today, its probably not a market with a long-term future that would be worth developing custom silicon for. Also, as you say, the 7.1 was never
that powerful c.f. more specialised PC workstation/server hardware, and what advantage it
did have was mostly courtesy of new - at the time - chips from Intel and AMD.
OTOH - even without developing new ML silicon. Apple could probably put 8 Mx Ultras into a 1U rack and use them to build nicely scalable clusters for cloud computing.