Technical evaluations aside, the longevity of a technology has more to do with the community behind it than it does with the suitability of the product. The "Sun surprise at railsconf Europe 2007" has shed some light on what the character of the Rails community may become. Justin seriously thinks this could lead to a hybrid Java/Ruby or JRuby coming of age in the near future.
That Ruby thunder is the Groovy rumbling we heard all summer. It looks like the "official" Sun Java camp may be backing the Ruby on Rails horse. In Open Source technology it isn't always the best, most feature rich, or advanced product that wins. This is probably the revelation that Sun is working from. Ruby on Rails is popular and Java can ride that train all the way into town.
The question is now, will JRuby ride its rails over Groovy or does Groovy still have a niche.
Moving from Java to Groovy is simple since most Java syntax works in Groovy. That means you only need to add on new language features and you're writing in Groovy. A very shallow and gradual learning curve for Java people. Is that enough? Is that everything?
JRuby's claim to fame will be the ability to work with EJBs and run in an "enterprise" environment. When that hype train comes into the station many things won't matter. When RoR is a full fledged member of the Java environment Ruby becomes one more Java DSL and Rails becomes one more Java web framework.
And that's a good thing. It means Ruby on Rails and Java are not mutually exclusive. It means both sides benefit. These are critical developments to watch right now because the fall out from these will greatly influence the political landscape of web development for years to come.
If Java can successfully bring Ruby into the fold we can reverse some industry killing fatal fragmentation.