Though I am not a hardcore fan of Dark Pit, I personally would not mind him getting in as a semi clone. Like the original poster said, Dark Pit's fighting style could be more brutal and offensive compared to that of Pit's. With the amount of weapons in Kid Icarus: Uprising, Dark Pit could easily be given a playstyle completly different from Pit's. For instance, Dark Pit could have somewhat similar normal moves due to him wielding the Silver Bow, but could have different special moves.
Here are a few idea's I came up with for possible moves. I thought of them not too long after I learnt Pit will be using the Upperdash Arm and Guardian Orbitars in Smash 4:
Standard Special (Silver Arrow): Dark Pit fires an arrow from his Silver Bow. Just like in the game, the Silver Arrow can be powerful up close, but lose power the farther it travels.
Side Special (Drill Arm): Dark Pit lunges forward, drilling into the opponent with the Drill Arm. This attack damages the opponent multiple times then sends them flying diagonally a little.
Upward Special (Wings of Icarus): Similar to Pit, Dark Pit is able to fly for a limited amount of time.
[collapse="Slight plot spoiler"]I was going to say Pandora's Flight, but since Dark Pit loses Pandora's powers later on in the game, I decided to just use Wings of Icarus.[/collapse]
Downward Special (Jetstream Orbitars): Dark Pit crouches, then on either side of him produces the Jetstream Orbitars. The Jetstream Orbitars blow away opponents and projectiles. Nearby opponents are damaged at the start of the move.
Forward Smash (Ogre Club): Dark Pit raises the Ogre Club over his head then brings it down on the opponent with bone-breaking force. Slow, but very powerful.
[EDIT]
Final Smash (Dark Pit Staff): Similar to Snake's Final Smash, Dark Pit flies off the stage and in front of the screen, then equips the Dark Pit Staff. Whilst hovering to the side of the screen, Dark Pit is able to snipe opponents with his staff. The shots are guided by a cursor, which is moved by the control stick. Each shot, if landed, sends the opponent(s) flying or kills them, depending on their damage percentage. Eventually, Dark Pit will fly back onto the stage, concluding the Final Smash.
The rest of his moves could consist of aggressive stabs and slices of the Silver Bow.