It's not ominous, it's strategic. Yesterday was about debunking Trump's narrative that Russia meddling was fake news. This indictment was designed to give Trump plausible deniability (for now) so the investigation can continue. That Rosenstein gave the press conference gives Mueller further cover. There was also the plea deal of Richard Pinedo, an American, announced yesterday as well, who had sold bank account and stole identities; make what you will of that, but I think it's connected to the Russia indictment. First step needed to be establish that the Russian's influenced the election, that legitimizes the probe itself; now Mueller has time to thoroughly make his case for collusion, which I'm sure is much more complex than what's publicly known.