I don't think Gematsu said Chrom was planned. They said Chrom was playable.
After the game was released, Sakurai said that Chrom was planned but a unique moveset made him feel kind of lackluster so he went back to the drawing board and chose Robin instead.
Also, I watched Alax's video on the whole blog theory, I've read the document but I'm still under the impression that blog theory rests on the assumption that characters are revealed all the way until the end (2.9 average, so 6 characters left as there are also veteran blog posts to cover still) . However, I had two people say that wasn't the case yesterday. So what's the deal-o? Does blog theory just assume they will reveal characters up until the release date or not?
G'day - spreadsheet guy here. If I understand what you're asking, you want to know if the 2.9 average characters-per-week will be assumed to keep up up to release. My answer to that is yes - sabi can go into the specifics on how the Blog's patterns have kept up consistently up until now, and I see absolutely no reason for the blog to trip up in the last weeks before release - it just doesn't seem like a marketing decision even Nintendo wouldn't reasonably make. Ultimate's main selling point is the sheer amount of content it's packing, with the Blog being one of the key communicators of that - having the whole thing go into radio silence for the last week of December would hypothetically grind that business strategy to a halt.
On the topic of broken street dates, I honestly think they won't make a dent in the Blog's schedule - like i said earlier, the Blog is an advertising campaign first and should be view as such. Why would any company in the right mind decide to halt their advertising in response to a few leakers or people getting the game early? It doesn't make sense in my eyes - broken street dates are a low level incident that haven't and won't have a butterfly effect that kills the Blog a week before release.
Finally, if there are dedicated Blog posts to the hidden mode's content (i.e. boss of the day) i wouldn't factor them in as something that would disturb the current trends. If anything, I'd put them on the same priority as items, assists, and pokéball pokémon - they fill in the gaps not filled by characters or music. Even if they did, I wouldn't be able to predict the effect they'd have at this stage - nobody knows how many bosses we'll be getting or if the new mode will even feature bosses enough to warrant separate blog posts about them. I agree that they could be the dark horse that beats blog theory into pulp, but I'm willing to double down on that for the time being.
Does that answer your questions? You can DM me @DuckMeat13 if you have more.