Now we now how that will happen: The Dominators are coming.
Created during the Jim Shooter run on Adevnture Comics, The Dominators are a conquering alien race that utilizes genetic manipulation in order to enhance their own abilities and conquer weaker planets. One of their most noteworthy tales was their role in the creation of the SW6 Legion of Superheroes, prompting a pretty great spin-off title in the process.
The Dominators were, of course, also the major threat of DC’s Invasion event.
Marc Guggenheim has stated that fans can expect to see the crossover “make use of cutting-edge prosthetics and computer effects to achieve a feature film-quality look” for the villains, and thusly it’s safe to assume the respective series will hew fairly closely to The Dominators’ classic razor-sharp teeth, lanky frames and red-spot sporting heads.
No other details have been released at this time, but seeds will surely be planted starting next week with the season premieres of The Flash and Arrow.