The market will decide. As someone said on HN: the best language in the world would be a mix of Go and D and would be called GoD. When there were few options, yes, it was enough to survive long enough to get a community. But when you have plenty of similar options, some of them backed by some major actors (at least in the early stages), i think no one will sacrifice his productivity (other than for hobby projects) for the sake of one language. I really hope D will develop into something, but looking to various sources (abandoned projects for D1 on dsource.org) on the net and google results, it seemed to me that D peaked somewhere around 2007-2008 with a slight revival in 2010 when D2 was released.
The drop after 2007/2008 probably corresponds to the Phobos/Tango debacle, and the fact that Walter decided to fork with D2.
One of the main problems was, he was almost the sole compiler developer, and could hardly keep up with the tasks of maintaining 2 parallel branches and developing new ideas at the same time. People complained that they couldn't get involved as much as they wanted. It's understandable that many people thought that D didn't have a solid future with such uncertainties.
Nowadays, these problems are mostly overcome with a much better organization: there are several committers for the compiler, and several committers for the standard library. Phobos is the standard library, it's maturing, D2 has shown its strengths over D1 and the community is united again, because not only it is deeply involved with the design of the language and standard lib(through the m-l), it is also involved with the implementation of essential parts of it. 2011 has been a very good year for D, and I think that more than ever, the whole project feels like it's going in the right direction.
edit: I guess another reason D isn't gaining as much traction as it could is, it has been removed from the Alioth computer language shootout. For a language which is aimed at raw speed (and was brilliant at that when it was still on the shootout), it's a severe blow.