Of course there are no guarantees. Anything could happen. Staal might not be as good as Chad Kilger either. Etc.
I used to think Tkaczuk would be nearly a shoo-in to make it too. I don't think his path was going too far wrong... good rookie pro year, he got some points in his brief time in Calgary... but the wheels fell off, and I guess there are lots of people who will point to issues away from his game on the ice.
Little... drives harder and plays more in the danger areas, IMO, but otherwise I suppose his on-ice performance is relatively comparable to Tkaczuk. Tkaczuk was thought of as a great leader and team player in his day too, so I don't know how to reconcile his subsequent troubles and use that as an argument promoting Little's attributes as a leader and character player. Little does seem to be very durable, but he also has a size disadvantage and who knows how many hits he'll take in the pros before he adjusts his junior stylings a bit to protect himself. So I don't think you could cross that off the list.
At the end of the day, then, there really is not much to say. I'm a big Little fan, and I think he'll make it. But the NHL Entry Draft has a Tkaczuk or Bonsignore or hundreds of others who you'll always be able to point to and wonder. I think it underlines the ever-increasing importance of off-ice evaluation and psychological evaluations too, something which most of us armchair HFBoards fans don't have much/any insight whatsoever into, which definitely cripples our ability to really split hairs when talking about the prospects.
I bet that didn't help you much, did it?