If we're really going to analyze every word that Sakurai says as direct confirmation that that is it then we need to take into consideration that Sakurai said "the stage total is turning out to be pretty impressive." And "now the total number of stages is 103."
I feel ridiculous saying that but I feel like we're taking everything too literally right now. I dunno, it totally could be the final number but I don't see what good they would do for themselves by locking themselves in a box with a specific stage number that would only allow for characters from already represented franchises to be revealed. Maybe I'm being biased because I want Isaac and Rayman and much more from unrepresented franchises but I think people are reading into this FAR too much.
I'm in the camp which believes we're not getting any new stage and that Sakurai was quite explicit about it.
"The stage total is turning out to be pretty impressive." Yeah I'm sorry but I have no idea how "turning out" suggests we could getting more. The word "total" is much more explicit. First is said "Let's compare it to the totals in previous games." then comes a chart comparing the number of stages in different Smash games (even accounting with and without DLC for 3DS/Wii U). The "now" is also not very explicit, because it doesn't necessarily mean "for now", the way it's used it feels more like a "grammatical binder" if anything, as evidenced by the French version of the Direct for example, whose translation includes no word that's literally translated as "now". To be fair the total numbers of stages mentioned for the Wii U version is inaccurate (48/56 instead of the actual 46/55) but considering the others are accurate it's most likely an honest error, and they're very close to the actual numbers anyway.
But the biggest thing against the idea of more stages is the "All stages selectable from the get-go", so if they've shown us the stage select screen (which they did) then we've seen all the stages. It's tempting to say only "these" stages are starters as said by the presenter, but the lack of this word in the caption suggests that "these stages" and "All stages" are the same.
So yeah, if you want to play on semantics, the evidence is overwhelmingly in favor of no new stages. The semantic 'evidence' for new stages is so weak that I had to put that word between commas in this sentence.
There also has been a point made about how the character count is no different from the stage count, but the difference is that we've been promised more characters (unless the "more announcements to come" only referred to King K. Rool but I really doubt that's the case), and there's no evidence that the current character count is final, whereas for the stages there has been in the form of the quite explicit word "total".
For this reason I doubt we're getting characters from new series not currently represented in Smash. I know this sucks because I understand so many people don't want to see Isaac/Rayman/etc. out of Smash Ultimate's speculation, but as far as I'm concerned the content of new stages is pretty much to this game what Ridley was to the previous Smash. Of course we could get characters from unrepresented series without their home stages, but while it's true that Marth and Roy came without a home stage in Melee, one was still planned, and aparently got cut by time constraints. Considering how few new stages there are in this game, you would have expected a Golden Sun stage for example to be in if Isaac is playable. Melee also had a much shorter development time than Ultimate. R.O.B. also doesn't seem to be strong evidence either as he lacks one not only in Brawl when he was introduced but also both versions of Smash 4 which suggests Sakurai isn't particularly interested in giving him a home stage (and there's no evidence for a planned but cut stage); considering R.O.B. is a real world peripheral it makes more sense for him to not have a home stage than a character from an RPG with its own lore.
I know this sucks, because Isaac could have been cool and I wanted Pokémon's seventh generation to get its own stage, but as far as I'm concerned my expectation for these are now close to none.
Also in the "Sound ► Series" section shown in the Direct, were shown series icons for series represented by characters and aren't "from one title rather than a series". More series could have not been shown yet and have to be unlocked, but considering all stages are available from start it would only make sense to have the music section for series without starter characters to be available from start. Basically if we get any new character from a currently unrepresented series their music is going to be in the "Other" section.
Asides from that I have a sort of crazy idea. Since Vergeben, who mostly gave us accurate informations so far, mentioned Minecraft content, what if the stage builder is Minecraft-themed, basically making the stage builder the Minecraft stage? Considering how Minecraft is all about terraforming I could totally see that happen. It's also a bit curious that we have not heard about the stage builder despite how much we've learned about Ultimate's stages. Most of all it would basically be a way for Steve to get in as a playable character despite the "no character from unrepresented series" logical conclusion I draw beforehand, since the stage builder is not going to be counted as part of the 103 stages (and is the only thing I expect when it comes to multiplayer stages outside of the confirmed 103), and as it would lack a proper stage Minecraft would have its music in the "other" section (which would also mean not many Minecraft musics but considering it's calm music which doesn't really fit a fighting game that would be fine, at least give us one more upbeat remix for Steve's trailer if he's in). Yeah I know it's a crazy idea, it's mostly speculation from weak evidence, so don't take it as if I'm genuinely expecting all of that to happen. I just can't wait to see this hypothesis inevitably debunked later... but if by chance this is what actually happens then I'm gonna be proud of it ahah.