No official announcement yet, but theater chains have already started to post the listings. With the MST3K Reunion next week, and Rifftrax promising two more Live shows this year, I imagine they will be announcing this next Tuesday. Sony has North American distributing rights, and I suppose that includes theatrical.
Hopefully the Kickstarter was a enough success that Rifftrax can purchase the digital rights too.
https://www.amctheatres.com/movies/rifftrax-live-mothra
Fathom Events and RiffTrax are partnering to present RiffTrax Live: Mothra. Join Kevin, Bill and Mike as they roast one of the most beloved (and bizzarre!) Japanese monster classics, 1961's "Mothra". It tells the story of a group of explorers who travel to a remote island, kidnap two tiny women, thereby inciting the wrath of a giant larvae which then swims the ocean, cocoons itself in downtown Tokyo, emerges as the titular Mothra and destroys everything in its path. Yes, it's a tale as old as time, but "Mothra" does it best! Live Thursday, August 18th.