In Can Ruby Live Without Rails?, veteran Java developer, Yakov Fain, interviews Bruce Tate, a famous Java-turned-Ruby developer who has become well known in the community for his book, From Java to Ruby. Tate tells Fain the five features of Ruby that he'd like to have implemented in Ruby, and explains some of the unique features of Ruby in a way that Java developers can understand.
Tate explains the strengths and weaknesses of Ruby in different programming fields:
Ruby is a fantastic applications language. I'm doing projects now with around 150 tables, a very sophisticated web interface [...] I'd do this project with 3 times the Java programmers, and it would take a little less than twice as long. [...] But all of this flexibility comes at a cost. I can't see Ruby as a platform for building middleware or operating systems. Enterprise programming (distributed 2pc, hard core orm) will take some time, and more investment than you see at this point. Right now, Ruby is a great applications language. I'd expect to see Ruby grow as a rich client framework. But it's not a one-size-fits-all tool.
Published by the Java Developer's Journal, the interview has a heavy Java-slant and doesn't dig too deep into the question posed in the title, but it's still a good read to see what one of Ruby's evangelists thinks about the future of Ruby.