1) Defensive Line
The starting line of Red Bryant, Colin Cole, Brandon Mebane and Chris Clemons was dominant when healthy last season. They ranked among the top 2-3 defensive lines in the NFL by all statistical measures. Injuries to Cole, Bryant and Mebane limited the duration of that dominance, but they did it for the first six games. Mebane is now a free agent, Bryant is coming off a knee surgery, and Clemons is creeping closer to 30. That said, this group has the best shot of any Seahawks unit to be dominant in the short-term. All it would take is a healthy Bryant and re-signing Mebane. Adding a Pro Bowl talent in the interior would super-charge this group, but Cullen Jenkins is probably the only free agent who fits that bill, and it's unlikely the Seahawks would go after him.
Earl Thomas is an elite talent, who has the combination of talent and work ethic to thrust him into Pro Bowl contention this season, and could reach All Pro status one day. Lawyer Milloy was a terrific compliment for the first half of last season, but he predictably wore down. The Seahawks have a young basher in Kam Chancellor who will be given the chance to step in and take over Milloy's spot. Chancellor can be special against the run, but we have not seen enough of him in coverage or blitzing to know how much he can be on the field. Mark LeGree was drafted this season as a back-up to Thomas, who could also slide in next to him in dime situations. The upside at this position is unknown right now. Thomas reaching his potential, alone, could make this a dominant part of the team.
ETA: 2011 or 2012
3) Wide Receiver
Mike Williams was dominant at times last season. Teams were powerless to stop him in the games he flashed 10+ receptions. Ben Obamanu is a nice compliment to him, and Golden Tate has the talent to be a roving playmaker. Rookie Kris Durham is an unknown. Adding a Pro Bowl-level receiver across from Williams would immediately vault this position group into elite status. That would be quite a transformation from the likes of Deion Branch, Logan Payne, and Koren Robinson from the past few years.
ETA: 2011 or 2012
4) Offensive Line
This group is so new, there won't be a single guy who has played a snap next to the man next to him when camp breaks. They are so green, the only city that would have them is The Emerald. That said, there is a lot to be gained from growing an offensive line together. These players have the chance to grow into a super power under the tutelage of Tom Cable and his staff. Okung has the same expectations as Thomas. He should be a Pro Bowler, and could be an All-Pro. The Seahawks, by all accounts, are going to add a near Pro-Bowl level left guard next to Okung. We all remember what a dominant left side can look like. Max Unger, John Moffit, and James Carpenter could be great, or could be busts. They don't all need to become Pro Bowl players in order to become a dominant unit. The 2005 Seahawks line had Sean Locklear, Chris Gray and Robbie Tobeck on it. Tobeck made the Pro Bowl that year, but he would never have gotten that honor if the team hadn't been so good. In other words, it was Walt, Hutch and three highly capable guys next to them that had hung together for a number of seasons.
Staring at a roster with exactly one QB on it, and a hopeless one at that, would seem at first to make this an odd position to include in a list of potential dominance. The truth is that teams without franchise QBs are the ones with the best chance of adding an elite one. Take Chicago for a second. They have Jay Cutler on their team. He will never be an elite quarterback, but he's also good enough that spending a high draft pick to replace him would be unlikely. Bears fans are stuck with him until the team gets a new GM, or he gets hurt. I would rather be the Seahawks looking for their franchise guy, then a team like the Bears who are stuck with a guy who will never be elite. All it takes is one great draft pick to turn a position of weakness into a strength. Look at St Louis, Atlanta, Baltimore and the like. Given that the team can't draft this guy until next year, and it usually takes at least two seasons to reach dominance, the Seahawks are still a few years away at this position.