I'm fairly clearly with Engels, Selma James and Mariarosa Dalla Costa on the function of the family—and therefore gender and sexual categories—as part of the system of social reproduction.
Smash capitalism early and you might see a breakdown in the bourgeois family and thus in heteronormativity. See Kollontai on plural economic relationships amongst mothers in her fantasy work where the POV character boffs a pseudo-Lenin.
That make me think of some comic art I saw... a Communist orgy, and it was not fully 'vanilla'....