I have been reading Carl Zimmer's book Evolution, The Triumph of an Idea and I have been startled about the similarities between the the Cambrian Explosion and the growth of declarative languages.
Just to recap (if you have not read the Wikipedia article yet) here is a quick summary. For the first 3.5 billions years, life on earth was mostly single celled animals. Then about 550 million years ago, the number of new multicellular complex-body-plan animals exploded. There are two salient reasons. First, we needed oxygen to breath. Before there was oxygen in the atmosphere respiration was not easy. Oxygen was a foundation for complex body plans on land. Second, life needed a genetic "tool kit" to build complex animal shapes. We needed the HOX genes for building complex body plans. After that happened, complex life forms did explode.
I am seeing the same thing appear in declarative languages. Declarative languages need foundations also. We needed ways for people to quickly create new languages (e.g. GUI XML Schema editors like XMLSpy) and ways to build consensus around the semantics of these new languages (wiki's, social networks, folkonomies and voting).
And next we need the declarative systems tool kits. Right now we have started to develop tools to allow XML Schemas to be quickly transformed into GUI XForms editors and we have XML databases that eliminated the need for complex middle tiers. We can put many of these tools in the hands of non-programmers and allow them to create domain-specific vocabularies and rule-based systems with GUI editors.
And when those tools mature we will see an explosion of declarative languages similar to the explosion of life forms 550 million years ago.
So what is your prediction? 1 year, 3 years, 5 years or 10 years from now? I think a small group of people could build this toolkit without millions of dollars of venture capital. There may even be open-source tools that do this in a few years. But I think the key is to combine the best of metadata registries, XML Schemas, transforms, XForms, XQuery and XML databases into a holistic declarative system.
And from here the many NEW ideas will evolve.