There is no official word that DC and Marvel are working on any crossover together. There is an open letter from Newsarama asking for a crossover, but neither DC or Marvel commented on it.
Being geographically separated miles away doesn't matter when working together in comics. Writer Brian Michael Bendis (Spider-Man, Daredevil, Superman, etc) is based in Portland, Oregon, and he has worked artist Sara Pichelli for years, even though she lives in Italy and the two rarely meet in person.
So for a while, an Oregon writer and an Italian artist worked on a comic based in New York City, for a company based in Los Angeles.
Many comic writers and artists don't live anywhere near New York or Los Angeles, but they all make regular contributions to the companies.
If a crossover were to happen, the teams can communicate by conference calls.