As a Roblox developer, it is currently impossible to make parts reflect anything but the sky. This can be problematic when the game takes place both outdoors and indoors and there are reflective objects inside. With the addition of PBR to Roblox engine, it would be nice to add reflection probes or voxel global illumination (using voxels to simulate light reflecting onto things and bouncing off of them. Kind of like realtime raytracing but before realtime raytracing and at a much lower resolution) as well.
If Roblox is able to address this issue, it would improve my game and my development experience because if I were to add reflective objects to my places (for example, make the floor on my field ice or metal) they would reflect objects around (such as the gates), making the game look better and more realistic (and lack of realism does not seem to be the current vector of Roblox in terms of graphics).