The Comey indictments are a real problem because they were obtained about three business days before the statute of limitations expired. There appear to be some mechanical defects in the way the bill was presented to the Grand Jury (or, as it seems, to the foreperson of the Grand Jury alone). Andrew McCarthy has an excellent explanation of this in National Review. If that defect is enough to knock out the indictment, you cannot go back to a Grand Jury and request new indictments. So, the Comey prosecution is in serious trouble. IIRC, there is still time to make another run at James. You need a properly authorized US Attorney presenting to a Grand Jury.
I think there could be some value in empaneling a special grand Jury regarding Comey, not to indict, but for fact-finding that could later be published.