I just uploaded a new release of my WiX XNA Installer template that has been updated to XNA 3.1!
If you happen to have a customized installer built on the XNA 3.0 template, fear not, for the required changes are very small! Use your favorite Diff/Merge tool and copy over any changes referring to Xna_3_1 into your existing installer.
I have declared this release a beta because I haven’t gotten around to testing it on all possible operating systems.