I'm fully expecting Chelsea Green to show up, maybe even as the mysetry opponent for Deonna Purrazzo. I wouldn't be surprised to see the IIconics show up, since they've said they'd like to stay together as a tag team and Impact is really the ony other company with a legitimate women's tag division.
As a refresher, here are the April 15th releases Billie Kay on April 15, 2021 Peyton Royce on April 15, 2021 The IIconics,Mickie James, Chelsea Green, Tucker, Kallisto, Bo Dallas, Wesley Blake, Mojo Rawley. Not exactly a Murderer's Row of men's talent, but there's certainly a nice crop of womens wrestlers to inject some life into other companies. Of course, Daniel Bryan is going to be rumored everywhere until when/if he appears somewhere, and wouldn't an Omeg vs Danielson match be a sight to behold? Ha, I wouldn't put money on that happening in Impact, though.
Or maybe CM Punk shows up?

And here's the card so far for Slammiversary:
World Title: Kenny Omega (c) vs. Sami Callihan
X Division Title Ultimate X Match: Josh Alexander (c) vs. Ace Austin vs. Rohit Raju vs. Trey Miguel vs. Petey Williams vs. Chris Bey
Knockouts Title: Deonna Purrazzo (c) vs. a mystery opponent
World Tag Team Titles: Violent By Design (c) vs. Rich Swann and Willie Mack vs. TJP and Fallah Bahh vs. The Good Brothers
Knockouts Tag Team Titles: Fire N Flava (c) vs. Rosemary and Havok
Chris Sabin vs. Moose
Eddie Edwards vs. W. Morrissey