tl;dr This lawsuit may have entertainment value for anyone amused by legal kookery; it is likely to disappoint in terms of having any serious impact on Scientology.
First, Peter Letterese is a known nutcase. His prior legal exploits involve threatening to sue every person online who had a copy of Steven Fishman's Lonesome Squirrel and the Fishman Affidavit, claiming it was defamatory. While Fishman's factual claims in Lonesome Squirrel are highly questionable and, indeed, probably defamatory, hosting the document itself is probably not going to constitute defamation. As he is suing about the copyright to Les Dane's works, he has already lost his lawsuit on this subject. It seems unlikely the court will allow the issue to be relitigated in the guise of a RICO racketeering suit.
Second, he may be pro se. While this is not always indication of being a kook, in combination with actually being a kook, I would say that this indicates a nearly 100% certainty of the suit being a kook suit, especially in this case, where Letterese has been involved in 78 docketed cases in federal and state courts, and 19 just in the last year and this year to date. It appears he is involved in ongoing personal as well as corporate bankruptcy litigation. Lately, he seems to sue Scientology, former business associates, and possibly other random people unfortunate enough to encounter him.
Regarding the pro se issue, the docket indicates he has a lawyer. The lawyer signature page is missing from the main complaint at Letterese et al v. Church of Scientology International, Inc. et al Document 1 - :: Justia Docs but if you look at the site, it's been incorrectly attached as the first page of "Attachment 1." It appears to be Charles D. Franken. I am, however, skeptical that any lawyer really wrote this. It reads exactly like other material written by Letterese.
Third, I've tried to read the complaint. It's virtually unintelligible. I defy anyone with or without legal training to read this document and ascertain what legal claims are being made. I doubt the court will be able to ascertain exactly what Letterese is talking about either.
I anticipate most of this suit will be dismissed under FRCP 12(b)(6) (failure to state a claim) as well as res judicata (i.e. this has already been decided). I wouldn't be surprised if Letterese is sanctioned for it, too, or ends up being ordered to pay the cult's costs. There's a claim in the complaint that Scientology has spent something like a million defending against Letterese's suits. Considering they are complete slam-dunk dogs, this is massive overspending, and they're unlikely to get it all, but they're likely to be vengeful about swatting a fly. They have so few wins these days that I suppose they really want to milk them.