The ex intel guys i follow have been saying that it will be a long time coming. So far, they have been right on pretty much everything so I am happy to back them at the moment.
Huge amount of info on all aspects. The hard part is:
You want to be 100% if you are going to accuse the president of an impeachable offence, let alone treason. The second issue is you need someone to roll over. Much of what is classified can struggle to be used. In addition, if the house or senate gives immunity to anyone (say flynn) then anything they say can't be used in an FBI criminal case.
So my reading of the tea leaves is that they are trying to roll someone, so they offer up someone higher up.
John Schindler has some very good articles about it (observer.com) and on twitter.