Show me a team with a great NFL QB that hasn't eventually unleashed him.
A good QB is the most valuable offensive weapon in football. When you have a player like that on your team, you don't waste him by turning him into a handoff machine.
Look at Brady, Ryan, and Roethlisberger. They began their careers as game managers, but eventually became high attempt passers.
I have no doubt that Seattle will want to remain a good running team, but this will eventually morph into Wilson's offense. It might not happen this year. It will happen though.
As far as the immediate outlook is concerned, I think Harvin will have every opportunity to shine here. It's the other guys Rice, Baldwin, Harper, and Tate who will be fighting for the scraps.
Eventually is the key word in your post. I agree that year over year for the foreseeable future, there will be a gradual shift to more passing attempts.
But relying on the running game and defense is a huge part of the current team's identity. Given that it was extremely successful last season, there is literally no reason for the Seahawks to change that formula substantially in 2013, unless something currently unforeseen happens, like significant injuries on defense or in the running game.
Wilson is great. But he excelled - and Seattle excelled - without many passing attempts last season. The team went 7-1 and averaged 34 ppg in the last 8 regular season games last season, while Wilson attempted just 183 passes - less than 23 passes per game. It is possible to have a high quality passing game without it being a high quantity passing game.
I will also note that I watched nearly all of Wilson's college games, since he played his first three seasons at my alma mater. His natural tendency is to spread the ball around rather than to lock in on a specific target. Naturally, the most talented players will get more targets than the others, because they will get open more than the others. But there will be no Brandon Marshall effect here.
I also think people are forgetting how talented Sidney Rice is, and failing to realize how good he will be with the opposing team now doubling or using their best cover corner on Harvin rather than on him. Similarly, Golden Tate as the #3 is also being underrated.