It's easy to predict Segura taking a step back next year (isn't that true of just about every player who has a breakout season, though?), but he's got a good glove for the position and fits nicely into the lineup with his pop and speed, with the added bonus being that he bats righty.
Losing Walker hurts, for sure, but his is a case of unrealized potential whereas Segura's potential is in the rearview. We've seen what he can do, and he's done it a couple of times already (3.5 WAR in 2013 and 5.0 WAR in 2016, per FanGraphs). The death of his son in 2014(?) was often discussed as a potential reason for his step backward in that year and in 2015, so there is legitimate reason to believe that the 2016 version is within the boundaries of what he can be expected to do in the future.
Fun, fun trade. Safeco traditionally swallows guys like this (~20 HR in the NL power) whole, but the plus (plus?) speed this guy brings to the table would seem to provide him with offensive options that a hitter like Cirillo, Aurilia, or their ilk don't have. Having the speed game to rely on should help keep the inevitable offensive doldrums from dragging him down like it has his predecessors.