Can you please provide a link to some doc on soyc report ?
Maybe a reporting plugin would be great for such features

Some documentation for SOYC is here:
http://code.google.com/p/google-web-toolkit/wiki/CodeSplitting

This would be a great feature to add. It'd be great to make this into a report, but just enabling the feature on the 2.0 Compiler is a starting point.

Creating report output has to be done with the output of the compiler, and would be a secondary step. There's a complication if a traditional Maven report is used, as the SOYC may not have run, in which case a re-compile would be needed to generate the reportable files.

I created an additional patch that adds many of the other parameters for GWT 2.0 support, including:
-soyc
-extra
-draftCompile
-validateOnly
-treeLogger
-XdisableClassMetadata
-XdisableCastChecking
-workDir

This patch also adds "recognition" of 2.0 via a GwtVersion.TWO_DOT_ZERO.
patch file name: GWT2.0-parameters.patch

patch applied with some few changes just as only code written by me is nice

soyc is set to true by default on gwt >= 2.0

a new Reporting SoycMojo is also in SVN