To me an appealing aspect of Ruby, Python etc is that I can pull up Vim, make some quick changes and see the results. For most Web apps this is a great thing.
Why would I move back to a statically typed, compiled, "slow to startup" runtime?
In my experience, Rails is much slower to start up than Java frameworks, even if the rvm itself loads faster. Also, Play does allow you to see changes instantly. Read the docs for more information.
As far as static typing goes, that's a larger debate. Many, myself included, believe static typing has many benefits for error prevention, debugging, tooling, etc.
To me an appealing aspect of Ruby, Python etc is that I can pull up Vim, make some quick changes and see the results. For most Web apps this is a great thing.
Why would I move back to a statically typed, compiled, "slow to startup" runtime?