As a Roblox developer, it is currently not possible to tile PBR textures. Right now, the SurfaceAppearance texture stretches across the entire mesh, whereas in many cases it would be better for the texture to tile, just like the Texture instance does.
A good method of fixing this is to add each of these properties from Texture to SurfaceAppearance:
This feature was actually announced by @Homeomorph back in June (6 months ago)
See #2, where he said that tiled materials would be coming. That was 6 months ago, and nothing has happened with this yet.
If Roblox is able to address this issue, it would improve my development experience because tiling PBR textures would be possible, and the SurfaceAppearance object would be functionally similar to the Texture object.