If we don't see KOS-MOS, but we do see Crash or Reimu, I'm not gonna know what to do guys.
Crash pretty much destroys the leak since Nintendo wouldn't hinge their bets on Reimu selling the audience alone at E3. Any out-there character is usually carried by a much larger presentation surrounding their reveal. Mega Man and Wii Fit Trainer come to mind, since they were unveiled at the time of Smash for Wii U and 3DS' reveal. Likewise, Palutena was introduced in the same event that gave us the world renown Pac-Man and the already-popular Miis.
Assuming the leak is legit, it would make sense to reveal Reimu and Crash together, since their duality would bring two different worlds together much in the same way that Hero and Banjo had some regional cross-over. If we get KOS-MOS tomorrow, that's a good sign for both Crash and Reimu. Maybe not necessarily
together in the way I described, but KOS-MOS is not an easy prediction at all given how overlooked she is. It's worth considering.
On the other hand, Reimu's reveal would make the rest of the leak 50/50 imo. Crash could still happen later on of course, but there's no guarantee the same will be said for KOS-MOS. Part of it has to do with the fact that the 5chan leak may be completely coincidental from here on out, and it's not like Reimu doesn't carry her own video game legacy.
In fact, it's worth noting that in the past year or so, the Indie community has slowly acknowledged her as a veteran figure (along with the rest of Touhou) into their Indie circle. Hypothetically speaking, her inclusion would be akin to Sephiroth's. In the same way that he's THE "Anime Swordsman", Reimu's THE "Indie Queen".
Honestly Reimu would be more of a positive sign toward KOS-MOS than Crash since everyone and their mom in the industry hinted at Crash
Not just Crash either. There's Rayman, Hayabusa, and Doomguy as well. I think they've been "hinted at" since base speculation. I'm more convinced that the public will eventually will them in Smash in some way, through some summoning circle ritual, haha. Hey, the more the merrier.