write metadata to source files of type jpg and dng

I know C1 states that source files will never be changed but in the file is the place where metadata is supposed to be.

We have the option to write the metadata to xmp files but other software won't read xmp files for jpg nor for dng. Why: because it is supposed to be in the file.
Yes, also for dng. Ask Adobe who published the description of dng files.

Al least add an option to write the metadata to where it is supposed to be for jpg and dng.