ThermalTake updated its Core X31 mid-tower case with a 4mm thick tempered glass side panel. You can find the full specifications over here, there are some small changes like a slightly higher weight and a change in the fan configuration, but overall it's pretty similar to the Core X31 RGB.
The tempered glass features 4mm thickness that guarantees the durability of the window. Moreover, the enlarged window design permits users to fully display and admire all components of the liquid-cooling system. Show off your dedicated set in the subtlest manner!
Pricing and availability is unknown but you can already find a Core X31 RGB for $99.99 so it's probably not going to be a lot more.