Darren Urban of the Cardinals' official website:
Andre Ellington is still the man. Rookie David Johnson, I’m guessing, will eventually have a role and there are other running backs who can help. But make no mistake, Ellington remains the linchpin at the position. He’s healthy and feeling good. He has to stay that way.
The Cardinals drafted David Johnson to lighten Ellington’s workload, and a reduction in touches may actually help his effectiveness, though it's unlikely to help his per game fantasy production. Ellington averaged 22.0 touches per game, but only managed 3.3 YPC after averaging 5.5 YPC in his rookie season. He owned the #10 PPG in PPR formats last year, so he can give up some touches and still provide solid RB2 numbers, especially if his per touch production bounces back.