Here's how the Falcons WR position should be:
1. Julio Jones
He primarily lines up on the outside. As the #1 WR that would normally mean that he lines up on the right side as the Z WR. But in the case of pairing him with Roddy, it makes more sense for him to be the X on the left side. Although moving forward the Falcons need to play him in both roles because he is going to make the switch the Z more than likely if/when Roddy declines. The benefit of this is that the team can put Julio anywhere on the field (including in the slot) and create matchup problems for the opposing defense similar to the way the Lions use Calvin Johnson.
2. Roddy White
He can stick at his Z receiver position for now, but when the team goes to 3 WR (anywhere between 60-80% of the time), he should be the primary slot receiver (Y).
3. Rueben Randle/Mario Manningham/Terrance Williams/Danario Alexander/Malcolm Floyd type
This player will be the primary backup for Julio Jones at the X, and in the 3-WR sets that will be his primary role (kicking Julio over to the Z). If/when Julio gets hurt, he becomes the starter at the X and still allows the Falcons to have a vertical element in their offense. This player should be 6-1 or taller and have sub-4.5 speed with good ball skills and a knack for making plays down the field. If this player is described as a one-trick pony (as Mike Wallace currently is or Vincent Jackson was once upon a time), then so be it. If that is the case, his one trick should be taking the top off a defense. And he needs to be a player that opposing teams fear can take the top off a defense. So that if/when they focus attention on Julio and roll their coverages to his side of the field, he'll be presented with a 1-on-1 matchup and will burn said corner in the same way that Roddy did in 2012. But the difference being this player is a lot more dynamic than Roddy was in 2012. The Falcons could easily find a player like this in FA (Manningham, Alexander, Meachem, Britt, Jerome Simpson, and Brandon LaFell all fit this description to varying degrees) or in this year's draft, which is deep at WR and typically is found in almost EVERY draft in Rounds 2 or 3. This is the sort of player that Josh Gordon could have been had we traded for him, and when the Falcons lost Jones for the season, should have been trying to find on the street or via trade. If this player is drafted, the eventual reality is that he will take over for Roddy 2 or so years down the road as the starter.
4. Harry DOuglas/Darius Johnson
This player is essentially the backup slot receiver. If any of the Top 3 players get injured, he will step in and become the slot receiver. If Julio or WR3 goes down, then Roddy will kick back out to the outside, and this player will man the slot. If Roddy gets hurt, then obviously he steps up and becomes the slot receiver.
In an ideal world, this player could also pull double duty on special teams as a returner (punts?), a role that both Douglas and Johnson have. Neither are great in coverage, which is a flaw, but you can live with it if either can also return kicks or punts.
5. Drew Davis
This player is primarily a special teams player, but should have the ability and capacity to contribute somewhat on offense in the event that the team is decimated on the depth chart. This player's primary value to the team is covering kicks and working as a gunner on punts, but again they should be good enough on offense and ideally versatile enough that they can play a variety of roles (outside or in the slot, which I believe Davis can do).
Eric Weems was a good example of the sort of maximum ability of this player (Weems BTW was a better WR than Davis is IMO).
6. Developmental WR
This should be a guy on your practice squad that has the potential to be the new WR3 if/when that player assumes the starting position for Roddy.
If the Falcons think a guy like Davis is anything more than their WR5, then…