Those are all good points. I didn't say I loved the idea, just that I didn't totally hate it. He hasn't looked good when centering Tarasenko before, for the reasons you mentioned. But I don't recall many times we have tried it. Maybe a few shifts here and there over less than 2 dozen games total. Given time to get acclimated, I would hope he would improve. The Steen centering others is also a good point, but at that time, we could shift Fabbri or Lehtera to center. I definitely want Fabbri to get some experience at center, I just don't want to give him 1C responsibility until we know how comfy he is there. It is also why I said we'd probably need to keep Lehtera or get another center. We'd need someone playing wing who could play center if Steen never adjusted.
As for trading him, what center would he get? We wouldn't get a better player given his age/contract. He is 32, coming off of surgery and possibly missing games, with only one year left at a fairly high cap hit that teams may not be able to fit. We'd probably have to lose out on net talent if we traded him due to those issues. I don't see NYI, who desperately need a winger, even giving us Strome straight up for 1 year of Steen. So while I am not opposed to trading him, I can't see a deal where we are a better team for the return.
Basically, if we cannot get a center in trade for Shattenkirk or in FA (which Stamkos is too much and Neilsen isn't good enough to make a real impact), Steen is, imo is our best internal option. Stastny clicks with Fabbri so I don't want to break them up, nor do I feel Tarasenko fits as the RW on that line. Lehtera isn't good enough. Steen is better than Sobotka, Berglund or Lehtera. Its not ideal but best of the worst so to speak.