Gail put the news out on Twitter, and it is up on Amazon. Secret Six Omnibus Vol. 1 is coming June '24.
The Amazon listing doesn't say what is included, but has the page count at 848. I'm guessing the Villains United Special, the 6-issue Villains United mini, the first 6-issue Secret Six mini, and the first 1 1/2 years (or so) of the regular series. That would roughly do it for page count.
I've kinda gotten turned off by the bulk of omnibuses, but I am tempted to get this when it comes.