Al Blue says that Groovy - unlike Python and Ruby (or Smalltalk) - isn't going anywhere:

It's clear that the next-generation language is going to be based on a scripting language that doesn't require type information to be entered. The adoption of (statically) untyped languages, like Python or Ruby shows that simple (and powerful) tasks can be done without the need for static typing information. However, it's a common misconception that these languages are untyped; in fact, they have dynamic typing, but don't require it to be declared in the language itself.

Creating a language like Groovy was supposed to bring scripting into the domain of Java users, mainly by peppering clean-syntax languages like Python with { and } symbols. However, rather than design the language (and then implement it), it's grown by hacking.