Let me just say this. Sing may be work out fine. That said, the reason the Niners needed Sing was because we did not have a legitimate threat at QB. We needed to win games the hard way. Those days are over. Smith is going to be very good for the next several years, so yes, the Niners could use a more offensive-minded coach.
One big problem...the coaches listed tend to like the West Coast offense. Does not mean they cannot adjust, but but does anyone here really want to risk tinkering with a good thing (Alex Smith right now). I don't. In my mind, Sing just bought himself another year based on the fact that he got Smith to become a real QB and was willing to change his offense to fit Alex. A lot of coaches will not do that.
Keep Sing and let this very talented team mature (including Sing). They are on there way. The future is finally, now.