I'm surprised Greninja's tongue wasn't talked about more before! There were definitely some rumblings, but it never really blew up... for whatever reason. I think it's an interesting point, but I don't think it's a hard deconfirm. Personally, I think it looks like the tongue is going behind Snake's launcher, but the image is too low quality to even really tell that. Like everything, I think it just adds to the wishy-washy and confusing nature of this entire situation.
That said, I can still see the mural being fake... though I think there's bound to be a really, really fascinating story behind it no matter what at this point.
If it is fake, with what's come out from "insiders" over these few days, my wager would be on the remaining characters being:
69. Isaac
70. Incineroar
60ε. Ken
71. Chorus Kids
(Though, numbers don't really matter here)
72. Geno/Sora (DLC)
Give or take a 38ε. Shadow.
This seems to jive the best all in all for me. This leaves us with a much more manageable 3 unique characters for base as opposed to the leak's 6-7 (including Incineroar) -- which I don't think contradicts
at all the statements about "a few" more fighters or "slowing down" reveals (if they are interpreted in a conservative sense). These additions also offer (imo) the most logical path. Incineroar jives with nearly everyone and months of rumors, Isaac is one of the only remaining "giants" of the request game (next to Geno -- and he's the only first party), and Chorus Kids were almost certainly nearly implemented in Smash 4, meaning they likely had several important moveset/visual assets already built and so were able to be implemented in this game fairly painlessly (and likely there's been desire to!) Ken, of course, is Ken. He's pretty much guaranteed no matter what.
Add or subtract Shadow depending on whether you think one more echo strains credulity or not. Geno/Sora being announced as a first DLC character jives with consistent rumors of a similar pre-launch DLC announcement like Mewtwo, and the consistent rumor of a Square Enix rep without adding another unique to base. This also gives the game a smooth 71 unique characters at launch, allowing marketing to
just use the fun and exciting phrase, "OVER 70 CHARACTERS!" if they're going by the numbers