Lightroom is capable to convert JPGs into DNG. The DNG Converter unfortunately currently is not. Please add JPG support to the Adobe DNG Converter. Thank you very much for considering!
Those of us who do time lapse work need this functionality, especially when working with images from sUAV, smart phone, and action cameras, where original RAW images may not be feasible.
I haven't read the entire 7 page thread, but it should be pointed out that a jpeg inside a dng wrapper is still a jpeg. I can't imagine what purpose this would serve.
One of the loudest cries was people who use astro software. I don't understand why they don't just hire a programmer or convince the ImageMagick folks to add this.
Again, as I said above: wrapping a jpeg inside a DNG container is a monumentally bad idea for many reasons. First of all, it's still a jpeg, with all the shortcomings of the jpeg format. The DNG container changes nothing.
More urgently, it's a false flag. A DNG is universally supposed to contain raw sensor data from a camera, not an already-destructively-processed jpeg. If jpeg is what you need, save as jpeg.