According to the patch notes, “Cross-Play is now here, allowing players on different platforms to group up and play Overwatch together! All console players are required to make a Battle.net account and link it to their console account.” This means that console players who do not yet have a Battle.net account will need to make one to proceed.
Even if you do not intend to take advantage of cross-play, Blizzard states that console players will still need to create an account. Also, keep in mind that cross-play won’t be available in all game modes, specifically Competitive. Cross-play will only support Quick Play, Arcade, and Custom.
According to Blizzard, Competitive mode will still split players up based on their platforms, meaning that console players will be matched with other console players, and the same will be applied to PC gamers. This is to help keep things fair since both console and PC gamers play using different peripherals, with some arguing that the keyboard and mouse is more accurate and would thus give PC players an advantage over console gamers.