I've been thinking a lot about this and I'm trying to wrap my head around the psychology for the leak and why it happened and who was truly responsible. I feel like there are three possible reasons this could've happened including three different responsible parties...
Scenario 1: The Grandson
The real leaker is Eric Bricard...the 3rd, grandson to Eric Bricard whom was taken on a tour of the facility by his grandfather and casually snapchatted a video of these promo materials to one of his friends, thus ruining his grandfather's career. Probably an early to mid-teen.
But I don't think this is likely, mainly because I can't imagine security would be this lax and I'm guessing Eric Sr. would've explained just how important it is to not take photos of ANYTHING.
Scenario 2: The Elaborate Hoax
I'm a cynic to the core and I don't trust anyone or anything until I've validated it personally. We only have it on the authority of a very small French gaming news blog (which doesn't even have its own website, just a blogspot) that ACP-PLV or Bricard were contacted. To me, that's not enough proof.
However, the reaction from all of the media outlets with ties to Nintendo, all of the "insiders" (who didn't know the full roster until recently and now suddenly know the whole thing so they can tell us it's fake), and youtube channels who have been starving for SSBU news in this two month dry spell and are for some reason willing to pass up on a GOLDEN source of ad revenue have convinced me the leak is real. APC-PLV's video showing the inside of their facility was even taken down (though not before people watched it and compared the printing the video showed to the printing in the leak).
Beyond that, if this is all an elaborate hoax, Bricard has a huge, HUUUUGE lawsuit he could file for defamation of character, especially because this is his livelihood.
So I'm leaning toward #3...
Scenario 3: Eric Bricard, Clueless Senior and Accidental Leaker Extraordinaire
Eric Bricard graduated in 1984, meaning he'd be somewhere between 55-65 years old today. I believe he did leak this, but had no idea the ramifications of doing so. Here's why...
Picture a man your parents' age. Someone showed him Snapchat, possibly a younger coworker, and while he knows how to use it, he likely doesn't know that Snapchat isn't really as secure as it makes itself out to be, as we all know it's possible to screen capture Snapchat video and photos. Eric likely didn't know this.
What Eric also didn't know is that Nintendo's strict security standards that apply to all of their promotional products, while seemingly asinine to him (hence the "**** Nintendo" message in the picture, complete with the "LOL" which is something an older person trying to be "hip" to social media would use), were in place for a very real reason. This may have been the first time ACP had worked with Nintendo, and Nintendo is very, VERY strict about how their products are handled (look up stories by 3rd party devs about Nintendo's exacting standards).
These standards were likely something Eric wasn't used to, and he also likely had no idea that the picture on this piece of promotional art was going to be such a huge deal because, being a senior citizen, he has no clue that there was an ocean of SSB fans desperately seeking news of any kind. In his mind, Nintendo was just being unreasonably strict, and I could see a Snapchat convo unfolding with a "friend" of his about just how stodgy Nintendo was about their promo materials and how it pissed him off.
He then sent a short video clip to said "friend", saying "lol **** Nintendo", assuming that Snapchat would ensure this short video was deleted forever moments later, and because I'm sure he had no idea that the internet would take the video and analyze the hell out of it in order to extract some very specific information.
All he saw was a picture of a bunch of goofy looking characters he'd never heard of all bunched together. He had no idea that the presence of 7 of those 70+ would blow up the entire goddamn internet, and even so, he figured that video would stay private, since that's what Snapchat is supposed to do and all, right...?
The friend haphazardly tried to blot out Eric's name (and got most of it) before leaking it on Discord (IIRC), and the rest is history. One disgruntled advertising associate who was sick of dealing with Nintendo's bull**** regulations about how their materials are handed decided to flip them the middle finger, not knowing the ****storm he was about to unleash.
We really need to start a Patreon for Eric if this whole thing turns out to be real. He made the wait leading up to SSBU the most memorable experience it could've possibly been, and I'm 90% sure he did it entirely by accident.