If the Cowboys are smart, they will have Elliot on a pitch count. If he turns out to be as versatile as many expect him to be, then it would be down right stupid to wear him out early in the season. There is no hard and fast rule on how long players can go in their first season in the NFL but typically, you see most players start running out of steam at game 10 or so. This is even different when a player is a starter. In first third of the season, I think it would be very wise to limit his carries to something around a 50/50 split with the other backs. I don't care how much you say he is the best blocker or whatever, the NFL game is different and he will have to learn blocking schemes. He will have to adjust and there will be things he hasn't seen before. That's just how it works and it's that way for everybody.
Remember, if we are fortunate enough to make the playoffs, the last thing you want is this kid used up. There is plenty of time to expand his role in the offense but those of you advocating 25 to 30 touches from day one really should consider his value later in the year, should we be in a position to make the playoffs.