yes, the point is if you converted and deleted the original raws then it is irreversible
So, show me were Adobe, Thomas Knoll or any of the Adobe evangelizers have advocated converting to DNG and deleting the original proprietary raw files? That's a straw man argument...if you understand long term preservation and conservation of digital objects you would want to store not only the original raw files but also the original software that can be used to open the original raw files. For long term sustainability the Library of Congress has outlined the main Sustainability Factors of Digital Formats.
Sustainability of Digital Formats: Planning for Library of Congress Collections. All of those factors really advocate the adoption of a raw file format such as DNG which can be sustained over time. There are already file formats that have been orphaned by the original manufacturer (like Kodak). Fortunately, Thomas Knoll reversed engineered those formats and allow access to those formats in ACR and DNG Converter.
the best proof that DNG conversion is not reliable (for backup instead of the originals) is that Adobe never produced an utility that can reverse their allegedly "lossless" conversion back to the original source
Horseshyte bud...Adobe released DNG Converter for the benefit of Adobe customers whose cameras were not supported by certain versions of software. There's no charge, it's free...as such it's an freeware software for the purpose of doing conversions...so, you want a utility to convert back? Why? In case you change you mind about converting? If you are so concerned about undocumented, proprietary file format metadata, why would you convert and delete your originals in the first place? I know for a fact a reconversion utility is possible...but there's little need to build and release one.
As it stands, DNG has been a valuable contribution to the digital photo industry–even if you don't think so. It was never intended to force any file formats on the manufacturers but intended to teach how a raw file format could store metadata in a fully documented manner. The fact that camera makers refuse to do the right thing by their customers and the industry is because too many people spread FUD for a variety of reasons...
DNG has been a gift to the industry...by the same guy that gave us Photoshop in the first place. Maybe a bit of gratitude might be in order? DNG is not perfect–nothing is. But if you find a problem with anything, Thomas is pretty responsive responding to legitimate criticisms–I've seen that in person so I know it is true.
BTW, The Library of Congress has made the following
Recommended Formats Statement. The Library of Congress Recommended Formats Statement (RFS) includes DNG as a preferred format for photographs in digital form and other graphic images in digital form. So, maybe people who do conservation and preservation for a living might have something useful to say on the subject?
So, that brings us to you...who are you? What is your name, what are your credentials and who are you to offer anything other than questionable opinions that may serve a dubious agenda? Care to enlighten us who you are and why we should care in the least what you think?