The biggest drawback of Cycles, since it’s already very fast, is memory consumption. Studio renderers like Arnold and RenderMan leverage .tx textures that are tiled and mipmapped so that they can use hundreds of 4k and 8k textures at render time but the renderer takes only a small portion of that data into RAM (VRAM) which is needed to render considering the size of an object in the frame and what’s actually visible.
Currently, you can select .tx textures in Blender and they will be rendered but it still loads the full rez texture into RAM as there is no difference between using .tx or .png in Blender apparently, regardless of the object framing.
Arnold and others consider the size of a given object in an image space when being rendered so they load only a small version of the texture for distant objects e.g. (it could be even some 32x32 mipmap or less regardless of the original resolution). And they also consider the visibility of the objects so that only those pieces (tiles) of the texture that are visible for the renderer, are actually loaded into the memory instead of the complete image.
Thus you can use 8k textures and not worry that much about RAM and especially VRAM which is much more limited. So my humble Feature request would be - Blender should fully utilize .tx textures and be able to create them like Arnold or RenderMan as it will affect every single Blender user and make Blender a bit closer to being a viable production tool.