His skating isn't a strength, nor is it a weakness. He's an average skater. Generates a decent amount of power, but doesn't possess great top end speed. Makes him a pretty effective player when driving the net, but less so in transition.
Biggest thing for Keppen is improving his puck play in transition, working on his ability to make plays at top speed. He's actually a good playmaker who has good vision in the offensive end. That's not something you always see from guys who play the way that he does. But again, his puck skill and confidence handling the puck will need to improve for him to take that next step.
I think there's a chance that he could develop into more than a 4th liner. Way too early to pigeon hold him to that. Do I think he could be the next Shane Doan and a future 1st line juggernaut? No. But depending on how his game develops, he could realistically be anything from an Andrew Ladd, to Blake Comeau, to a Scott Kosmachuk, who's well rounded skill set never really allowed him to find a permanent role in the NHL.