I'm pretty sure LPDDR4 is already used, even LPDDR4X which is a slight revision with a lower voltage profile. They can be found in a lot of high end smart phones.
LPDDR is basically just Low Power DDR, the main difference will be power consumption, especially in standby.
Comparing LDDDR3 and DDR4 though, assuming the laptop's RAM speeds are similar between the two, then yes there won't be much performance difference. If the DDR4 kit offers faster RAM speeds then I'll go for that especially if you're using integrated graphics.