Every other company is jumping into the pistol caliber carbine market. With the expertise at S&W, they could sell a fine carbine in .45 or 9mm easily! Ruger, Sig Sauer and PTR all see the advantages of a carbine, why not S&W?
I would really, really like to see a 9mm carbine that takes M&P mags.
But only if it is reliable. It seems like a lot of carbines use a blowback action and just are not as reliable as I would want. I was pretty excited about the Ruger carbine but from what I have read it would make a great range gun but would not be reliable enough to be a home defense gun.