TV Guide managed to grab a scoop on where Arrow will pick up on its return next Wednesday, and I'm excited to say the least. You don't want to read any further if you want to go in blindly, but I will say this spoiler doesn't really do more than set the stage.
It appears as though Felicity will be leaving Starling City to go aid Barry after his "accident", which comes at a terrible time for Oliver as there are now multiple villains to be worried about. Hopefully this means Felicity will be jumping back and forth between the series and being the bridge between the two shows when Flash gets going. I'm not one for the whole Oliver and Felicity romance and would much rather see her go on full time with Flash...but I can see how and why that would never happen. Next Wednesday we'll see it all go down, and hopefully more of Slade in the current timeline!