Trump has bad mouthed the FBI over and over.
The GOP were trying to avoid the FBI. if they had wanted them, they would have had Trump call them in. They didn't do that. They were trying to fast track it. So I do not see how this is good news for them or the FBI already would have been involved.
Some of the letters from the witnesses were written by their lawyers. It's difficult to nail them on perjury. But if they say the same thing to the FBI and are caught lying .... they go to jail. As well, a bunch of witnesses would not trust speaking with the GOP and probably trust the FBI more as non partisan. The FBI is more likely to get more of the truth out than the process to date ... which is probably why the GOP didn't want them.
Up to now, the GOP have largely side stepped the other allegations with broad verbal brush offs. The FBI have to look at Avenatti's client, Ramirez and one or two of the other anonymous claims - which is likely to give each of them more visibility and credibility.
While that is going on, in the face of what nearly just happened, more folks are likely to come forward.
Also, a number of Kavanaugh's statements may be exposed as lies by this investigation.
and it may provide a foundation for criminal charges to be filed in Md - where even Kavanaugh admitted the statute of limitations would not curtail them in Md.
Lastly, Gamble v US may be getting under way soon after Oct 3rd. Kavanaugh won't be there Oct 3rd. That may be a major depressing development for Trump because his children and others would not be able to escape state prosecution.
Time will tell soon enough but I doubt this is good news for Trump et al