It's pretty simple really. The in-game smash website (the way the game shows you stuff like events and pop-ups, ect) can be accessed through any old internet browser since, well, it's just a website. By inspecting the images you can see that each news post, spirit event, and tourney is assigned a number and they tend to go chronologically. For whatever reason (despite seemingly not doing this before as I've just checked) the official Nintendo website posted images from the last Smash photo contest using the same filenames as they would have on the ingame website, which tells us the post number is 103. And since it doesn't line up chronologically, as the last news post was number 91, the only explanation for such a large gap is that a batch of posts coinciding with an update is coming.
Based on past precedent (if you can't tell, I've been keeping track of this seemingly pointless knowledge for awhile now) let me try and stitch together what the post order could/should look like. We've got 11 slots to work with.
- 92: Version 9.0.0 Coming Soon (posted a few days before the update to warn people about replays)
- 93: Software Update Available : Version 9.0.0
- 94: "Fighter 7" Challenger Pack Available for Purchase
- 95: Fighter Pass Vol. 2 Avalible for Purchase!
- 96: Mii Costume 1
- 97: Mii Costume 2
- 98: Mii Costume 3
- 99: Mii Costume 4
- 100: Mii Costume 5 (?)
- 101: Mii Costume 6 (?)
- 102: Exclusive Offer For Switch Online Members (?)
- 103: 9th Photo Contest Results
For the record, I'm somewhat unsure about the last 3. The last 3 characters all had Exclusive Offers For Switch Online Members released alongside them, so we can reasonably assume that's what one of the last 3 slots is. But the other 2? The only reasonable thing to assume they are is Mii Costumes, and 6 has been our limit so far, though we haven't had a character come with 6 since what, Joker? Though that was before stuff likely started getting moved around... don't read TOO much into it, since there really isn't much to get out of it, but I think we can atleast partially assume 7 is indeed coming with 6 costumes. Hmmm.