Your definition of open-platform requires that the code not be covered by any patents. Anyway, the best thing that can come out of all of this is more deep-pocketed players angry with the software patent system.
I don't see the Linux kernel devs getting sued or suing the *BSD kernel devs, although they share ideas all the time.
Also, people scale/modify the Linux/BSD kernel to fit their needs all the time. The Java patent grant only applies if you're not building a subset/superset of Java or if you're extending OpenJDK. But these aren't enough ... some people do not want GPL.
That's what I mean by "the spirit of open-source" ... it's a collaboration effort from which everyone benefits.
And as of this recent announcement, OpenJDK is open-source only by license ... if that wasn't clear already.
OpenJDK is safe because AFAIK the GPLv2 license also has a patent grant.
But if you want to take Apache Harmony and trim it down so it fits on a mobile device or on a pen ... the very essence of open-source ... then you're fucked.
If you want to take some idea from OpenJDK and use it in Jikes; a cross-pollination of ideas (not copyright infringement) which is again ... the very essence of open-source ... then you're fucked again.
Java is not an open-platform. It never was.