Mark Guggenheim, Andrew Kreisberg, and even Berlanti himself have previously stated that crossovers between SG, Arrow, and Flash are possible (I believe Berlanti has previously responded in the affirmative after being asked this question directly).
We also have The Hollywood Reporter and Entertainment Weekly having made statements (off-handed though they may have been) indicating that the issue of whether or not crossovers are POSSIBLE has in fact been settled, but that the focus is not currently on planning any crossover between the series.
We'll see, though.
We also have The Hollywood Reporter and Entertainment Weekly having made statements (off-handed though they may have been) indicating that the issue of whether or not crossovers are POSSIBLE has in fact been settled, but that the focus is not currently on planning any crossover between the series.
We'll see, though.