Marvel is currently making a killing with their expansive network of movie tie-ins, which I assume is what prompted the Arrow/Flash tie-ins (behind the scenes). DC is also coming up with Dawn of Justice, which sets up at least three more members of the Justice League.
Unfortunately, the Arrow-Verse has been heavily modified to not have any meta-humans (with the exception of the Flash, which is treated as unusual). This actually works out pretty well given its format (TV shows with supernatural effects tend to suffer from poor special effects, and although by now the Arrow-Verse probably has the budget for it, it was a wise move not to start that way).
There is obvious incentive to tie these together at some point, but it seems unlikely given the ground rules established in the first two seasons of Arrow. Superman and Wonder Woman would clearly bend the no-supernatural rule, while Green Lantern (John Stewart FTW) and the Martian Man-Hunter would break it completely.
TL;DR is there any plan to expand the Arrow-Verse to include the rest of the Justice League? Will it tie in with the new Dawn of Justice movie, or will that be a simultaneous, but separate, franchise?