Originally Posted by huzzug
That shouldn't be much difficult considering there are 7(?) different versions of Skylake i7 mobile performance processors that differ based on the graphic processors alone.
You have 7 different skylake i7 mobile chips, which come with different tdp, core count, speed and gpu. Now add 3 version for each chip, one with 8GB of HBM2E, one with 16GB, one with 32GB. That gives you now 21 chips.
This will escalate prices.
Allowing to connect extra DDR4 memory, will directly make the memory much slower, which will completely negate the whole reason to use HBM2E.