Three things to keep in mind, Volomon:
1: Space. You cannot possibly fit everything in, we'd be talking about a 2.000 page book.
2: Core HAS to be simplified! The more complicated extra options aren't what you want in your core book. Insect Spirits are complicated, just like Toxic stuff, Genetech, Vehicle and Weapon Modifications, Arsenal, Advanced Lifestyle, Background Count, Chargen Alternatives, and so on and so forth.
3: I am not aware of ANYTHING being pulled out of Core compared to SR4. (Except Skinlink but that one is gone forever.) Instead, they even put a few more things in instead. Background Count, Insect Spirits, karmagen, all those weren't in Core to begin with in SR4.
They follow the SR4 style of books, except that they're combining Arsenal and catalog books into Run & Gun and Rigger 5. There will be an Augmentation book, there will be a Matrix book, there will be a Runner book, there will be a Magic book. They're not deliberately removing things from Core, they're simply following a decent "Basic Core book and Advanced Extended Core books" structure just like in SR4.