http://zap2it.com/2016/07/wbtv-comic-con-live-blog-arrow-the-flash-legends-of-tomorrow/ Confirmed at Comic Con. So here everyone was expecting Aquaman or Batman, they've pretty much gone down the opposite route. Of course being the Arrowverse it's Malcom Merlyn, Damien Darkh, Captain Cold and Reverse Flash. They will be the lead villains in the next season of Legends of Tomorrow and are going to be "time douchebags" make of that what you will.
A few nice hints and teasers there, including that, yes, Arrow will be (slightly) affected by the end of The Flash. Interesting. Not so sure about Legends, though. Four villains could be fun, but couldn't they come up with new ones? Why just recycle the old ones all over again?