I wouldn't be surprised if the report was requested to prepare for discussions of the Nation Right to Carry legislation that's been kicking around Congress for a few years.
Bingo! Feinstein's press release
when the GAO report was issued makes it clear that she wanted official documentation supporting her longstanding contention that other states have less stringent concealed carry requirements than California (image that).
Feinstein also makes it clear that she strongly supports states rights with respect to fighting a federal reduction of gun control ... but not so much regarding a federal increase in gun control.