It seems like a whole lot of people are concerned about the massive narrative consequences of what mechanics are being previewed first for a play test. For example, the most recent blog post set off an argument that really isn't at all about the mechanics of what the new system will be like, it is about the order in which some material will be revealed and supported with future supplemental material, and the consequences that will have on how these decisions will shape the narrative arch of the pathfinder universe.
I actually think this is a fascinating problem because the default assumption here is that "core" implies the game is playable from only one book. This has not really been true of very many RPGS and there is now an assumed triumvirate of books that create a new "core": A player's handbook, a DM guide, and a Bestiary.
The way to make sure you get the material you want in the new system is not to fight anyone down in a play test blog reveal forum, but to offer ideas and suggestions for new ways all of this material could be presented, so that the game opens up for everyone's play style to be accommodated (or as many people as possible).
Maybe it is a good idea for the new pathfinder system to consider whether old models of establishing what can and cannot be considered a part of its game are the most appropriate or not, but no hardly seems like the time to build up jaded walls of "not in my pathfinder."
For a playtest, it makes sense that Paizo is pushing everything they can into one book (for accessibility sake), and hopefully a lot of the material they give us is the material that they are least certain about, because that is what needs to get tested and played with. But that doesn't mean the construction of "core" pathfinder needs to be limited to the increasingly outdated model that one rule book establishes the entirety or even the centrality of the pathfinder universe. Maybe, when it comes time for feedback later, we as players can push for something like a first Ultimate Ancestry book to be one of the first supplements, and the "core" rulebook could even narrow down to less ancestry options (maybe 6, or 4 or 1 or even none), so that more class options, feat options, or other material could feature right away. Maybe the core book centers on one specific city or region and only provides the most necessary material to set a campaign there? Or maybe people can keep tossing out other ideas until a great new one comes together?
The more ancestry, background and class fit modular design principles and contain less fringe "this ancestry/background/class operates entirely on its own set of rules," the easier it will be to add more balanced material later. Either through ERATTA (which will hopefully be avoidable by adequate and advanced play-testing like they are trying to allow for now) , or by making more material optional for different gaming tables to decide what options they want to use in their own games.
But all of that is past the scope of a playtest.
it makes a lot of sense for the play test to include really new stuff that the development team wants to test for playability and not be trying to make their play test stuff fit into the most conservative model possible, because they already have a pretty good idea of what people want from the most basic fantasy tropes.
Please, keep showing us the weird, the creative, and the different stuff that is in consideration for this play test, there will be plenty of time later to discuss how it works in game play, when we actually get to play with it.
Look at it this way: we still have several months to bleed ourselves dry of this ornery cantankerous argumentative disposition that has been so prominently on display on this forum since its inception.
Hopefully that will mean the real playtest will have slightly less of an angst and spleen content.
Personally, I'm hoping the playtest book is complete enough that I can use it for a homebrew sandbox campaign for a year. Anything more than that is just gravy.