I have considered it deeply. Many of our enterprise systems are Java-based, so JRuby's ability to call Java methods directly without implanting services would be a huge pragmatic boon. But every time I consider that I have to balance it against being able to use a constellation of gems in Rails. For example, nokogiri (libxml) is used in a ton of stuff. Sure there are Java equivalents, but that isn't the issue. Rather I would have to reimplement or find replacements for everything we use that depends on that without introducing side-effects. In my experience that's really hard unless it's a toy application without many dependencies. (Read: opposite of most enterprise Ruby apps)
Also, as a gem author I've tried to support jruby along with MRI, but it requires jumping through a lot more hoops. Of course any cross-platform code requires more work to support, but it's a pressure on small devs. If no one needs it, no one helps support it, so then it becomes another gem that is effectively MRI-only. Kind of a viscous cycle.
Nokogiri natively supports JRuby, no equivalent searching required.
CExts are basically the only place where this issue really pops up and all the major CExt gems (Like nokogiri) support JRuby.
Ruby also suffers from the lack of a formal VM, so other implementations are merely similar rather than being guaranteed to run all programs. This is not the same with JVM vendors, where choice of IBM vs Oracle is largely based on extrinsic features rather than intrinsic compatibility. (Or at least you have to get in really deep to find differences-- in Rails you usually find incompatibilities that stop you from even starting the app).
The deal breaker for me is the very slow startup time for tests and no gains for run once scripts. I've seen people developing with MRI and doing CI on JRuby to work around that. It's worth doing that only if you have a service running with some real load. Most internal services do nothing almost all the time.
