That's not Google's choice. Sun and Oracle are the ones refusing to allow the Java trademark to be used by an open-source implementation for a mobile platform.
I think Oracle would allow it if the price was right. The problem is that "one Java" probably means Java SE, which means you have to use bloat like JAR files and Swing/AWT, which would make Android less competitive with iOS.
Would it really help if someone paid $Nbn for the Java label for some snapshot of Harmony or whatever? Open source software (which is open in spirit, not just by name) is always a moving target. As soon as you fork it, it's no longer covered by the license. And when is it a fork, exactly?
I don't think anybody's talking about a snapshot. During the Sun/Google negotiations there was discussion of an ongoing partnership where Google would be forced to adopt new versions of Java as the JCP released them. Google didn't want the JCP backseat-driving Android, so they declined.
The problem isn't just trademarks and API compatibility. I just wish Android could run a true JVM. Problem is the JVM spec is only licensed to TCK compliant implementations, and those aren't given to un-licensed mobile implementation.
Google quite intentionally steered away from any certified or branded Java because they wanted Sun asserting no control over them (in some of the "Damning" evidence there were internal discussions where Google talks about ignoring licensing not because of financial costs, but because it put Sun at the wheel). J2ME was the disaster it was because of Sun's guardianship.
Android is not Sun. It borrows from some of the tools out of convenience, and uses some of the conventions, but no one is under any illusion that it is the same platform.
