I'm cherry-picking a little, taking the offense from this year and the D from 08 which was when he last played consistently at SS, but he's not that far from achieving that potential, and I honestly believe he has the ability to surpass it.
Why not play it safe? Because there's more to gain than there is to lose. If you take that risk and it pays off, you have a puncher's chance to have the best SS in the American League, especially if Jeter does NOT rebound. Maybe even if he does. Point is the competition for offensive shortstops isn't precisely stiff at the moment and Lowrie can probably lay claim to the title with an .800-.850 OPS, 12 HR kinda year, which we already know is something he has the talent to do.
Besides hitting better than Scutaro when healthy, Lowrie's also quite a bit better defensively. Even if he doesn't have the kinda offensive year I'm projecting, Lowrie's no slouch as a defensive SS and could justify his role on that basis with a ..700-750 OPS and still be one of the better all-around SS in the league. The standards are that low right now, a chance to overshoot those standards by as much as Lowrie could if he has a great year should be seized with both hands.