Well, one of my choices is this 1976 dubbed Russian version of “The Little Mermaid” - titled Rusalochka - see here: Perfect MST3K Movie - "The Little Mermaid" - 1976 Russian Movie English DUB!! - #6 by Rusty0918. Has the same cinamatographer as “422: Day the Earth Froze.”
I would really like to see them do a bad animated movie. It would be new territory for the hosts and the 'bots. They did sort of go partly into this with that Gumby short “Robot Rumpus” for the “912: Screaming Skull” episode, but I’m sure there are plenty of bad animated movies they could do.
Maybe they should also try dibs on a silent movie. I have one recommended - 1929’s “The Manxman” (and yes I know who directed it - but it does NOT diminish the pain in any way).