I've followed this project on r/UnearthedArcana for a few months, and much like another reviewer, I too am a huge fan of dragons. My interest in all of it started when I found the Half Dragon player race on the subreddit. I hadn't found a post as in-depth as Niels' in my previous searches, and to see one with as much attention to details as this one I fell in love with it immediately. I would make comments on new pieces of draconic content up until its release, expressing my excitement for it, even though I do not have a group to use it in. I personally don't believe that you will find any better Draconic homebrew content than what Niels has put together in this compendium. And to know that there's possible expansions to this in the works just makes me excited to see it if and when it comes out.
The only thing I have to say is that I wish I could take a peek inside Niels' headcanon of a world with his draconic races and lore in it. I would love to read a more in-depth story or lore book based on the works in this piece. They give smaller discriptive background information in some of the subclasses' origins and the cultures of the races, but I would love to see some deep lore in the form of either just a story/lore book, or maybe even a full adventure setting, if not an entire campaign module for this work to be used with. Of course, this is only a explaination of how I'd love to see more, but that's because I love this so much and the small bits of lore that's given in it.