Well the i7 X-series are desktop CPUs, so unless you want 2 minute battery life and your lap boiled alive, they won't be coming to the MBPs.

If you mean the mobile Xeons then that's not likely either as performance for those aren't
that great and comparatively falter in single core.
You're right about the balance between hardware and software. Many Apple Pro applications take advantage of multicore, such as LPX and FCPX, so it would be able to utilise the power. However with OpenCL and especially Metal, a dGPU is far more beneficial.
Whilst it's mostly a good move to have more choice for consumers, it's a slightly surprising move from Intel. At those kinds of prices and niche uses to actually justify that amount of horsepower, you'd likely be looking at a dual Xeon setup anyway (the i-series never used to be dual socket compatible, though not sure if that's changed with the x-series). So it seems to be a little redundant, but hey, it's people's money to spend how they want.
Generally more is better but macOS' memory management and software/hardware optimisation is second to none, so you don't need to keep throwing updated hardware at the OS just to keep it running close to how it should be. As such you can be reassured that if that CPU was added into a Mac product, the OS and bespoke Pro Apps would support it and utilise it effectively.