A fun letter appears in the Justice League of America #5 (Apr 1961), in which Bob Cherry of Detroit, Michigan calls on DC comics to up their crossover type events and weave their characters much more tightly together.
Clark (Superman) Kent, Lois Lane and Iris West interview Carol Ferris and Hal (Green Lantern) Jordan on a new type of airplane. Bruce (Batman Wayne and Oliver (Green Arrow) Queen meet at a party. Barry (Flash) Allen and John (Martian Manhunter) Jones meet at a policemen’s convention
Bob Cherry’s letter in Justice League of America #5, April 1961
The editor of the JLA letters column uses the opportunity to make a bunch of “fruit” puns, but it’s unclear to me how this idea lands with them.
Frankly, I love all these ideas, since it increases the realism and verisimilitude of the comics universe as a whole. Characters would naturally and incidentally meet each other. Marvel Comics takes this idea and runs with it a few years from now once they have magazines with ongoing characters. This makes sense simply from a marketing / advertising perspective. The Marvel Cinematic Universe took this to a whole other level, basically guaranteeing continued billion-dollar box offices by injecting actors as superhero cameos throughout their films and properties.