So a couple of things that have been bothering me ever since OSL and Arnold got introduced is the interoperability.
One example is that alot of the amazing features that OSL offers are simply incompatible with Arnold GPU, BitmapLookup, UberBitmap or the newly added OSL HDRI Maps which shipped with Max2021 are not working when rendering with Arnold GPU.
Also some Arnold maps are displayed inaccurately in the viewport or not working at all f.e. Arnold Image, Arnold: Color Correct, Arnold's Normal Shader or the basic Standard Surface Shader in combination with Specular/Gloss or Metal/Roughness texture maps.
Now there are alternatives to alot of Arnold Maps f.e. OSL math maps or old legacy maps but rendering with arnold internal maps is significantly faster.
And while most of the things that bother me are not breaking they would be great quality of life improvements.
