DC and Marvel will very likely never do another crossover again but it's fun to imagine. Anyway what crossovers would you like to see?
Artemis/Sif/Valkyrie - All three are warriors connected to myths and are supporting characters of their universe's respective main myth hero Wonder Woman and Thor.
Donna Troy/Angela - Retconned in siblings to the aforementioned Wonder Woman and Thor.
Captain Atom/Hulk - Both gained their powers from radiation. Both deal with the military. Both have nemeses who are U.S. generals.
Lady Shiva/Elektra - Martial artists and assassins who alternate between being heroes and villains.
Icon/Blue Marvel - Both are different takes on "what if Superman was black".
Cassandra Cain/X-23 - Both are teenage girls raised as assassins.
Black Widow/Mademoiselle Marie - Both are redheaded European intelligence agents.
Etrigan/Ghost Rider - Hosts to demonic forces.
Shadowpact/Midnight Sons - Magic teams.
Creature Commandos/Legion of Monsters
Artemis/Sif/Valkyrie - All three are warriors connected to myths and are supporting characters of their universe's respective main myth hero Wonder Woman and Thor.
Donna Troy/Angela - Retconned in siblings to the aforementioned Wonder Woman and Thor.
Captain Atom/Hulk - Both gained their powers from radiation. Both deal with the military. Both have nemeses who are U.S. generals.
Lady Shiva/Elektra - Martial artists and assassins who alternate between being heroes and villains.
Icon/Blue Marvel - Both are different takes on "what if Superman was black".
Cassandra Cain/X-23 - Both are teenage girls raised as assassins.
Black Widow/Mademoiselle Marie - Both are redheaded European intelligence agents.
Etrigan/Ghost Rider - Hosts to demonic forces.
Shadowpact/Midnight Sons - Magic teams.
Creature Commandos/Legion of Monsters