Stepan also isn't your typical playmaking center... at all.
First, he's average at faceoffs. Has been every year. He's got decent but unspectacular pivotal skating, good vision, but only just above average passing ability. He isn't very strong on the puck, either.
However, he has shown great hands around the net. Deflections, goal mouth plays, you remember at least a few of them. Some of the players he has clocked best with were of third line caliber, as he seems to do best on the cycle rather than the rush.
So when you guys say he'll be the absolute center for a guy like Nash, always play that position, I don't know if Stepan is the guy you want him to be/ think he is. He's not Oates or Savard or Crosby or even Richards. He reminds me a lot more of a hybrid Pavelski/Stastny and I think he'll consequently see substantial time on the wings in his career.
I disagree with a couple of your assertions, here.
First off, I think Stepan's passing ability is well above "average". His passes are hard, crisp, and on target. He's not going to be putting up any 80+ assist seasns like Thornton/Sedin, but I don't think 45-55 assists per year is out of the question at all, especially if he's playing with a talented goal scorer like Nash.
Secondly, I think you underrate how good his vision is. That, along with his hockey IQ, is his best attribute. He sees the ice better than any other player on the team.
Third, I think he's a career center. His defensive game is far, far too good to be wasted on the wing. A lot of his offense comes from being so sound defensively, he's able to break up plays and turn it the other way, especially shorthanded. He had a Selke caliber season last year, and was much better than the heralded Callahan has ever been defensively. I agree with you that he's not a Savard or a Richards, but for different reasons. I think he can have 75-85 point seasons, for sure, but the style of play is different. He isn't flashy, but he's about as impeccable a positional player as you'll find, and I think that it allows him to adapt and mesh with whoever is placed on his line. I do think that he is an excellent fit for Nash, as well, because what Stepan lacks (size, strength, net drive ability), Nash has, and what Nash lacks (vision, positional awareness, defensive ability), Stepan has. They offset each other wonderfully.
Last year, Stepan took huge steps forward with his skating, his shot, and his strength. I was watching some footage from the 11-12 season and it's remarkable how much stronger Stepan is on the puck while skating through the neutral zone than he was during the 11-12 season, and his shot/release capabilities are night and day. Young players improve. The argument against Stepan seems to be that he's going to decline simply because the possibility is there.
I think Stepan is a very unique player, and I see no reason why he can't continue to
improve, let alone maintain his play from last year.
Long story short, Stepan was an excellent 1C last season, and certainly has the ability to keep his play moving forward and solidfy himself as arguably the team's most important building block up front. It's going to be a wait and see kind of thing with him, and I'm perfectly fine with seeing what he's capable of. It's called patience and development, and it's what built good teams like Boston.