There are two parts to this.
As with Java, there's the laguage, and then there are the libraries.
Ruby 2.0, which is being worked on now, is an evolution, not a revolution. Not too much will change for Ruby programmers--the biggest shifts are in the underlying implementation. I don't see the laguage itself growing.
So, then, what's to stop Ruby having the same kind of library explosion suffered by Java. In theory, nothing. But, in practice, there are a couple of factors. First, we don't have the JCP. That means we don't have comittees designing things. Many features of
J2EE are the result of compromises at the comittee level (OK, you can add entity beans if I can have cmp, or whatever). Most Ruby libraries are still the result (at least initially) of individual developers scratching itches.
But, you're right. This is something to fear.
Dave