I don't think that people would want to be stuck with Ponyta as their only Fire-type option again.
Only Manaphy was part of a regional Dex and necessary for completion. Granted you got it through a book and didn't need to own it but it still was a part of the Sinnoh Dex. Manaphy is the exception to Mythical never being necessary for completing a regional Dex.
Manaphy was only necessary for Platinum because they tacked the new additions onto the end instead of renumbering the Dex like later games have. The Dex will probably be renumbered this time if they use Platinum's expansion, and Manaphy will be moved to the end so it's not needed.
Well this is the first region they're remaking where the third version had a dex expansion, so there's no real precedent for whether they use the original's or third version's dex. But considering HGSS and ORAS was willing to add in cross gen evos that were introduced since the originals and the dex expansion was a response to significant issues with the first games' dex, I don't think they're that dead set on being that faithful to the originals that they'd reopen old wounds or exclude 4th gen Pokemon that probably should've been there in the first place (looking at you, post game cross gen evos and legendaries). They seem to draw the line at adding in new families that weren't there before, you most likely won't see the likes of say, Litwick or Salazzle in the Sinnoh Dex and you probably won't see stuff like Growlithe or Vulpix either (unless they just add everything in the game to the Sinnoh Dex and they're not actually accessible until post game), but anything else they can do to fix dex issues they seem to be willing to do. Cross gen evos and regional variants have already been in, third game expansions aren't really much of a step up from that.
To be fair, 7 extra Pokemon isn't much of a difference from Platinum, that'd be pretty underwhelming. It's still a far cry from the larger, 300-400 Pokemon regional dexes of recent games. Totally expected, but still underwhelming.
Three of those appear in Sword and Shield, not two (Cresselia, Heatran and Regigigas).
Right, and I agree with you on that, but in terms of being an exciting, tangible expansion, 7 extra Pokemon that were just post game legendaries isn't much better than not having anything more than Platinum's 210 at all. What people are probably going to be looking for to get excited is something along the lines of at least 25-50 new Pokemon available in the main game or a selection as expansive as say, BW2, XY, SM, USUM, or SwSh. And considering Game Freak's track record of not changing the dex much in remakes (even in games where they fully had the opportunity to like ORAS), and the game being described as a faithful remake, it's highly unlikely that's going to happen. So the overall point that you shouldn't get your hopes up for the Sinnoh Dex is a good one, it seems wise to do so.
My only concern about Porygon-Z being revealed is that it could have been the player character's Pokémon.
Because they could've imported it from HOME? I can see that, but I reckon it's in the dex.
Not quite--the trailer shows the statue in Eterna City as being a combination of Dialga, Palkia, and Arceus, so there may be some sort of Kyurem-esque fusion going on here:
