Bit of both. Current Intel chips (including these ones) don't support LPDDR4. This is largely because Intel is at this point years behind on their roadmap; phone chips have supported LPDDR4 for a while. They support LPDDR3 and plain (non-low-power) DDR4. So if you want to go over 16GB, you have to use plain DDR4, and power usage, especially suspended power usage, suffers.

Next-gen Intel chips will support LPDDR4, making the whole thing a bit of a non-issue.