...16 GB on the air cooled XTX is nice for the price but I stopped using LuxRender a while back as the interface to the software I use is buggy as all get out and I moved on to Iray (that only supports Nvidia's CUDA language) which is a lot more stable.
The only thing I can hope for is this will prompt Nvida to come out with a competitive enthusiast card. Currently the only HBM2 memory GPU card they have available (also 16 GB) is the Quadro GP100 which retails for about 6,500$