Actually, they are rather speedy in adopting new CPUs. Its just that the CPUs are often released in waves and the tier that Apple uses is not available yet .
A separate mobile Vega will certainly be as fast as the on-package Vega M GH, just less power- and space-efficient. So yes, these packages are ideal for Apple. In fact, I hope for a Coffee lake + Vega package. Should't be a problem for Intel probably, they just need to replace the CPU die...
You are being too optimistic here. The CPU/GPU package alone will probably cost more then $500...
Maybe yes, maybe no !
Well if intel can sell it's NUC for 1000$ for a product they know will not be sold by millions, I'm sure Apple can also make it for 1000$. The price that Intel ask for, includes the developpement cost which is a lot higher than what Apple will be able to ask per/product.
Actually it wouldn't make sense to ask 1500$ for it since you could get a i5 8th with 4 core from a Macbook pro which would be similarly priced, with screen, battery, but no GPU yes.
Yes you are right they always use the higher end ones.. But yet the price is higher for no much difference. I never understood why they were doing so.
I would love to see a 8th 6 cores + Vega package however I doubt it will be possible for now. Maybe next year..