This has been the problem plaguing Russia reporting all along. The media has no direct knowledge about what is going on, so they’re relying on leaked information, even though some people have an interest in taking down Trump while others are interested in vindicating him.
Once the report hits, we’ll get anonymously sourced stories suggesting that Trump committed impeachable offenses and others claiming the report offers full vindication.
If the actual report is released, people who choose to read all the materials can judge for themselves whether the gathered evidence supports a given conclusion. And even if the average news consumer won’t actually be digging through potentially thousands of pages of Mueller’s documents, the fact that they are publicly available will act as a check on the proliferation of fake news through anonymous reports.