LISAsoft was able to get a subset of GeoTools working on the Android platform.
The following are some notes if you would like to repeat and extend the experiment.
Pluggable Factory System
The Factory SPI system still works in android; but uses the official Java 6 technique of FactoryLocator (rather than the "internal" Java ImageIO FactoryRegistery system which we use).
The solution is to make the GeoTools factory system pluggable
This same work is needed for good OSGi support.