The facts:

• Sun and many other organizations have started considering moves to Mercurial. In Sun's case, it's a mandate for all Sun-managed OSS projects (OpenSolaris, OpenJDK, etc).
• Moving projects to Mercurial frequently (usually?) requires IDE/tool support.
  
• Sun's IDE/tools and those of many other organizations are Java-based (NetBeans, Eclipse, and so on).
• Mercurial is written in Python.
• Jython is an implementation of Python for the JVM.

Therefore, Jython Mercurial support would be an excellent vector to Mercurial adoption within Java organizations (Sun included, I'd wager). Corollary: getting Mercurial running on Jython is an excellent business case for contributing time and resources to Jython.

Put simply: if you want to become an OSS rockstar tomorrow, get Mercurial running on Jython.

(credit for this idea goes to OpenJDK ambassador Tom Marble...I'm just trying to needle the OSS world into making it happen)