PC Perspective reports Allied Control had an immersion cooled mining rig on display at the SuperComputing 2017 conference.
You can view it in the tweet below, it's a two-phase immersion cooling system with a water cooled condensor coil and the 3M Novec fluid. Novec is a non-conductive fluid with a boiling point of just 41°C. This fluid costs over $100 per liter and needs to be hermetically sealed so it's easy to see why this isn't going to go mainstream. But still, it looks extremely cool!
Nick Knupffer (@Nick_Knupffer) posted a video (embedded below) of the cooling system in action cooling a high end processor and five graphics cards. The components are submerged in a non-flamable, non-conductive fluid that has a very low boiling point of 41°C. Interestingly, the heatsinks and fans are removed allowing for direct contact between the fluid and the chips (in this case there is a copper baseplate on the CPU but bare ASICs can also be cooled). When the hardware is in use, heat is transfered to the liquid which begins to boil off from a liquid to a vapor / gaseous state. The vapor rises to the surface and hits a condensor coil (which can be water cooled) that cools the gas until it turns back into a liquid and falls back into the tank. The company has previously shown off an overclocked 20 GPU (250W) plus dual Xeon system that was able to run flat out (The GPUs at 120% TDP) running deep learning as well as mining Z-Cash when not working on HPC projects while keeping all the hardware well under thermal limits and not throttling. Cnet also spotted a 10 GPU system being shown off at Computex (warning autoplay video ad!).