1. DDR4L Not finished yet.

2. Intel wont support LPDDR4 until 2018.

Unless the Intel or the memory industry works with Apple in tandam, I dont see how 32GB can be achieved without,

A. Apple making their own SoC or switching to AMD.

B. Simply switch to same clockspeed model of Kabylake while using Desktop memory. The increase in Desktop emory power usage will be offset by Kabylake's power saving.

or C. The return of 17" Macbook Pro.