Sunflower 11/02/2021 (Tue) 13:24:26 Id: 72d2a5 No.171 del
>So if there is already a new earth and new humans, what's the point of all that talk about being pushed away and kept and all the other stuff here. I assumed this place here was to become the "new earth". Will both earths eventually merge or something?
Over time, timelines are split into branches forming a large tree structure. When it reaches the end point at 200k years, the tree is too complex and will collapse. When this happens time and space collapses back into one timeline and one space. All smaller loops that kept people trapped also ends and time becomes one coherent unit again. This is how Yuuka explained it.

Before the collapse, the creators of the new earth will decide what parts of the old earth they want to keep and transfer over. They will create a list of what individuals, what genetics, what cultural elements etc they want to remain for historical reference. Those are then woven into the new earth's history as it begins.
Time and space are our references for what is real, so we won't notice anything while in this "corridor" as long as the essentials are kept in place. But anything outside of our lives has been removed. That's why you see so many NPCs now. Time within our timeline moves seperatly from the new earth's time so we won't perceive it outside of regular time progression. It's likely some version of the CERN created collapse will still take place, and at that moment we are merged into the new earth. All things Gensokyo doesn't want, like modern architecture and whatever, will then be deleted.
The pendant
was just created as an experiment to see if it would work, Yuuka could already decide who should remain. Having that device just increases the ability of the wearer slightly. Because it's only emulating the function there is nothing saying you can stay permanently with that one. Maybe you can stay a few years or one lifetime, depending on how aligned you are with the new earth. Getting a reincarnation spot on a planet with a population of 100 000 will be very difficult.