I can see what you mean but usually with the stock art they rarely have the Pokemon "attacking" at you. I think the hand has just been "fused" with the back hair, as if you look at the bottom of the back hair it's curved in a that it looks like the arm is there (and the "bump" that seperates the rest of the back hair with the ponytail could be its actual hand). As for the ear, in my opinion it looks too think to be an ear. But for all we know you could be right, sometimes the art they show for a movie isn't actually the stock art the guides and online Pokedexes are going to use.
Hey, all I want is for Ash to get a Riolu, there is no need to call me names. 
But on the subject of a higher evolution, the idea came to me that maybe checking the stats of each Pokemon might help us get a clear picture of who might be getting an evolution (though of course we'll also view the possibilty of a split evolution). We'll first list out the stats of both of the pre-evolutions of the two candidates, Riolu & Poochyena:

Name: Riolu
HP: 40
Attack: 70
Defense: 40
Special Attack: 35
Special Defense: 40
Speed: 60
Total: 285

Name: Poochyena
HP: 35
Attack: 55
Defense: 35
Special Attack: 30
Special Defense: 30
Speed: 35
Total: 220
We'll first cover Lucario, we'll list down his stats and write down the cases of what a Stage 2 Evolution and a Split Evolution can bring.

Name: Lucario
HP: 70
Attack: 110
Defense: 70
Special Attack: 115
Special Defense: 70
Speed: 90
Total: 525
Stage 2 Evolution: Lucario is no doubt set in the Attack stat is doing good in all the others. If this is a Riolu-family line Stage 2 evolution then most likely what would increase is either the most is the defensive stats (Defense & Special Defence) or the often overlooked stats (HP & Speed).
Split Evolution: Now being a Split Evolution focuses on mainly switching the attack stats with the defense stats, this would probably be the case here. The other two stats (Speed & HP) may or may not change of change places with each other, though there aren't usually the focused of Split Evolutions.
My Opinion: If this is for the Riolu-family line, I'll have to say a Stage 2 Evolution makes a bit more sense as this Pokemon looks wild and agile, something you'll expect to strike and run off and strike again. Therefore the main focus is attack stats and also the Speed stat.
So Lucario's case is a bit iffy due to Lucario having good evened-out stats, but now let's give Mightyena its time in the limelight:

Name: Mightyena
HP: 70
Attack: 90
Defense: 70
Special Attack: 60
Special Defense: 60
Speed: 70
Total: 420
Stage 2 Evolution: While right now Mightyena has NO WAY of competing with Lucario (and Mightyene being a type that is weak to Lucario's main is just the icing on the cake), an evolution on the other hand might boost its stats up greatly. As things stand, it looks like Mightyena is more physical based so those would be the stats (Attack, Defence, & Speed) that'll get a great increase with Special Attack & Special Defense getting a smaller increase. HP is on par with Lucario's so a little increase there wouldn't hurt either.
Split Evolution: As I said, Mightyena is more physically based, so a split evolution would concentrate on a special base (Special Attack and Special Defense).
My Opinion: Once again I'm going with the Stage 2 Evolution if this is for the Poochyena family-line. They need that stat boost that only a Stage 2 Evolution is going to provide them, plus a strike-and-run looking Pokemon would be all physical in what it does, as if it had a good Special Attack it wouldn't need to strike-and-run but rather just blast from far away.
Boy you can just feel the Lucario & Mightyena supporters gathering up and ready to declare war on the other (with groups suppoting a new Pokemon altogether or a Legendary unfortunely not being that big). And this is only with one of the new Pokemon, how would it be like when we begin being shown the other 99 + "Secret Legendaries"! All I can say is that there better be more Fire-types then Generation IV had.