In my limited experience with them, DGCR is superior to the PDGA and UDisc course directories in many ways. Certainly in the ways that matter to me. I don't see a merger changing that.
In the long run, who knows? If they create a better mousetrap, a better course directory that DGCR, it will be a pretty awesome one, indeed.
What makes DGCR great is the user contributed content is so much better than any of those. For whatever reason timg has managed to create a system the encourages quality reviews and quality content. Sure, there are a lot of crap reviews here but the percentage of good reviews and content is far superior. I've used Udisc frequently for scoring purposes and also finding courses. While the scoring function is great there is a lot of garbage as well. On one particular trip had I used DGCR instead of Udisc I wouldn't have wasted an hour driving to and from a non-existent course a few months ago. Sure, they might be able to create a larger directory but IMHO it will never have the quality content that DGCR has.