Currently this is possible after built-in images are loaded in memory. Allows to save memory used by dependency graph and copy-on-write. In practice this lowers peak system memory usage from 52GB to 42GB on a production file of spring 03_035_A.lighting. Note, that this only applies to F12 and command line renders. Bigger note, that this optimization is currently only possible if there are no grease pencil objects to be rendered.