I expect both to play significant roles in Atlanta, provided each can stay healthy. Truth is, NFL teams don't use featured backs the way they used to; having Coleman and Freeman—two different runners who are both scheme fits—is important for this offense.
I think any time you rely heavily on one guy, there's added concern about potential injuries. Jones has been dealing with a sore hamstring, but when he's putting up such ridiculous numbers, it's hard to be too worried about that particular ailment. He's a better receiver at 80-90 percent than just about everyone else is at full health.
If I had to pick one thing, it'd be pass defense. The Falcons are now 25th in the NFL in this area (they're allowing 282.3 yards per game through the air) which is in line with how they fared in 2014. The run D is much-improved thanks to the new scheme and several front seven acquisitions, so if the backfield progresses, it'll be tough to move the ball against this team.
It definitely has more to do with the former. Atlanta's schedule hasn't been overwhelming, but it's not like the Eagles, Giants and Cowboys are pushovers. The Falcons have made substantial improvements on both sides of the ball and, without a doubt, deserve to have a winning record.
Has to be the O-linemen. Houston's defensive front—led by J.J. Watt, Jadeveon Clowney and Vince Wilfork—plays at a higher level than the three Atlanta's faced so far in 2015. Whether or not the Falcons move to 4-0 could depend on whether or not Matt Ryan is given the time he needs in the pocket. The OL has certainly exceeded expectations so far, and it'll have to hold strong again this week to move the ball.
Nick Williams and Justin Hardy are similar WRs: speedy, good at running short and intermediate routes, capable of returning kicks/punts. Right now, it appears the Falcons think Williams is more ready than Hardy, which is not entirely surprising. Hardy is still young, and it's difficult to get playing time when there are six other receivers on the 53-man roster. His time will come, though.
Now that NASA has confirmed water exists on Mars, the latter seems very possible.