I'm curious about the performance compared to something like, say, the RTX 3070.
The neural engine is small and inference only. It's also only exposed by a far higher level interface, CoreML.
Where it could still make sense is if you have a small VRAM pool on the dGPU and a big one on the M1, but with the price of a Mac, not sure that makes a lot of sense either in most scenarios compared to paying for a big dGPU.