PC World just published this article: Want 32GB of RAM in your laptop or NUC? You can finally do it | PCWorld
Quite expensive though. The modules are available here: https://squareup.com/market/MemphisElectronicRetail/imm-g-d-lsod-ag-b-e-1
This will only work on NUCs with 5th Generation Intel CPU, so the NUC model part# must begin with NUC5i...