It would be immensely helpful if it was added. I'm especially interested in such an option being available in Batch PDF output, along with with pdf quality option (which was added recently to single pdf export).
The quality option is already available in the Batch PDF output. You can specify the image quality in a field called "JPEG image quality". The quality value should be between 0 (low quality) and 10 (high quality). If you generate a batch command file you should see this field along with usage instructions.