Per this thread (Discogs as metadata source) Roon won’t be implementing Discogs as a source and have not identified any other databases they will add in the near future.
Make of that what you will, but I’ve been thinking about asking for a refund for a long time. I’ve been using Roon for about 3 years and I’ve seen no development in these glaring problems which is just unacceptable in a “premium” product.