Executive producers Marc Guggenheim and Wendy Mericle told IGN that Season 6 will move on to explore flashbacks from different character perspectives beyond Oliver, and also might feature some flash forwards in time. Guggenheim confirmed during the 2016 summer TV Critics Association press tour that Season 5 will be the last Arrow season to use flashbacks as a regular device.
“Last year, when we sort of realized we’re going to go past Season 5, we basically made a collective decision that Season 5 would be the final year of flashbacks. Next year, in Season 6, what we’ll end up doing is we’ll do some episodes without any sort of flashbacks.
Source and more: IGN