Sorry, now I understand what you meant. My feeling is that the planet is already in 4th dimension, and us too, but there are forces, very strong in the 4th dimension, who have prevented us for thousands of years from accessing to our talents. I call them dark lords, and I saw them in dreams and shamanic sessions. So either we step up or we have to fight those forces, which are a projection of ourselves of course. In my experience, I've never been able to defeat my dark side by fighting it, but by changing my level of perception, that is by stepping up.
I find it intriguing, what you say about who's going to stay and who's going to leave. I've always thought that the ones who would be ready to ascend to a new dimension would leave, but I like much better your idea that they would stay and step into the other side together with Gaya. (Of course all this is speculation and imagery, it is very probable that whatever happens, it will be surprising)
Do you know Robert Monroe? he was the first to have out of body experiences and write about them from a modern perspective (he also changed the name from the previous "astral projection" into OBE). He mentioned visiting some of these parallel realities in 3d, where people who had died didn't relize they had died and continued to live their life (generally a "hard" life) as if nothing had happened.