Because of Marvel and DC's success, everyone wants a shared universe now, Sony tried and failed to launch a Ghostbusters shared universe, and Universal is gonna give it a try with a Universal Monsterverse starting with the Mummy, but these would both be grafted after the fact, what are some true shared universes that Hollywood could adapt.

Valiant is a given and supposedly in development, most of the shared universes I can think of come from the world of gaming, the various Dungeons and Dragons settings (Forgotten Realms, Dragonlance, Greyhawk, Ebberron, Ravenloft, Spelljammer, Dark Sun) Warhammer 40K, Warhammer Fantasy/Age of Sigmar, White Wolf's World of Darkness (Vampire the Masquerade, Werewolf the Apocalypse), I'd probably consider HP Lovecrafts Cthulhu Mythos a shared universe at this point due to all the games, movies,novels etc. etc. that have used it.

Any other Shared universes that I haven't listed.