Yes, there are different versions of DNG and different options, but Adobe defines DNG so LR would always support all options.
Now, DNG is a flexible format, so makers could add their own tags, in effect extending the format.
There is also something called linear DNG, which is demosaiced. Not a good thing in my book.
Would camera vendors unite around a single raw file specification it would make life simpler for a lot of people. Also, Sony developing it's image data converter is just insane. The software is of very little use and they give it away free. So, where is the beef for Sony. Competitive advantage? No! Earning money? No!
Good point, John. But am I mistaken in thinking that even with DNG there are "varieties" on offer? Is Phase's DNG the same as everone else's? It's a genuine question: probably the differences are in the metadata area and don't really affect the image quality?
And I agree Erik. If the maker's software was up to the job then we probably wouldn't have LR, C1 and a few other good converters to choose from.