Alright, I've got some new evidence.
So if the in-game pics are fakes made from a brawl mod then there is no doubt the mod that would have been used is this one
I happen to be the maker of Shulk's mod moveset, so I've spent a large amount of time staring at this model. As you can see, it's over Ike and the move being used here is Ike's up smash. More specifically, it's Shulk's model ripped from Xenoblade and rigged over Ike's skeleton. Shulk has not been rigged over any other character, and the other models of Shulk look exactly the same (literally) except that they use different forms of the Monado.
You can see there is a spec of light on his right (our left) cheek. This is an issue with the lighting on the model, and depending on the angle you look at it it either looks brighter than the rest of the skin or darker than the rest of the skin.
This is key because if this model were to be shown in an up close shot, it could be easily distinguished by this lighting issue. As it happens, the leaker provided a photo where the face is visible to a degree, although, still low quality. Take a look at the left side of the face and if you can see the lighting issue.
Do you see it? It just happens to be right by the nose on the left side of the face, right by where the mod has its issue.
Although, the pose is something I've never seen before, but it's something I could create using brawl box. Anyone that creates brawl mods could do that by just moving the bones around in brawl box. This isn't absurd either, since the leaker would have had to mod the game to create the other photos. RED TEAM and the background would be done with photoshop, which is not out of the question since the person would need to be good at photoshop to do the leaks posted through 4chan.
Well, enough of that for now. Now, let's look at the Shulk in the game.
The first thing that comes to mind with this is Ike's jab attack. Here's this recreated in the game (I tried to get the angle right but it's not perfect):
They really do look similar. The body is angled in the same way (accounting for how the leaked photo is tilted) and the punch looks the same. There are some differences, however. The right arm is in a different position and in the one photo the Monado is on Shulk's back. However, this change is something even an amateur to photoshop like me could do, especially with the blank, snowy background behind Shulk in the leak photo. The other things I notice are in the leak, the shorts on the right leg look a lot baggier than they do in the brawl mod. The left foot is also in a different angle.
Disclaimer: I'm not claiming that the character (Dunban rigged over Link) is what the leaker used for Lucina. He's just there because I needed a second character to join the game.
The other thing that comes to mind as a potential move being used is Ike's grab. Here is this recreated with the mod:
This image also gives a better view of the snowy background, which has its own differences from the leak. I'm not going to discuss that in detail.
The arm doesn't look as good here, but the legs do. The right leg's shorts looks baggier like with the leak and the left leg is at a more similar angle. The arm/Monado could still be edited with photoshop.
Neither of them look exactly like how the leak does, but it is possible for them to be combined with photoshop.
I would like to close off by saying I'm not biased either way in this, and all I care about is the truth. As you can see by my avatar, Shulk's my number one wanted newcomer, so I would be more inclined to be biased for him than against him anyways.