My theory on Eywa's plan
Silly thought but I've been thinking about what Eywa's plan is regarding the RDA and humanity and wanted to share them.
To preface this, I believe that Pandora lived in a situation parallel to earth and went through events that led to the near extinction of the Na'vi. Somehow, during that period, Eywa and Pandora would have become one, granting her the knowledge to save Pandora, the Na'vi, and later become the Great Mother.
Having lived something similar in the past, She could understand, at first, why they sought shelter in her home but the destruction they brought later on is not something she can tolerate. Having forbidden metal weapons, this put her and her children at a disadvantage in some combat and force her to find an edge that doesn't rely on those.
Grace, being a scientist and joining the spirit world, could grant Eywa the edge that she needs to win.. Jake has shared about Earth with Eywa and showed her the consequences of humanity but, as a soldier, he could not show her how it worked but Grace could.
And so, I believe that Eywa, working alongside Grace, could create a tree that could breathe new life into earth but would demand enough change from them that they would not be able to return to Pandora. It would be growing in abandonned yet unharmed facility, as the tree would need to live on our air. It might be why she only acts against the RDA on certain occassions, as she needs them presents to send it to Earth and why her plan seems to take a long time.
I also believe she would target Selfridge with that plan; she knows of him through Grace and Jake's eyes. With Ardmore's death, all that remains at the top of the RDA ladder on Pandora is Quaritch and Selfridge. The former being a whole other discussion.
Selfridge's return to Earth after Avatar branded him a black sheep and a disappointment to both his family and the RDA. And although he is a greedy man who see profit above all, he is also someone who cares about optic and was reluctant to violence at times. He feels that he has to succeed and prove himself to his father, and thus won't return home without good reason.
What better reason is there than the salvation of earth and humanity itself? He could return home a hero, dwarfing even his father and the RDA and branding himself a hero.
A son for a son.
Earth gave Eywa a new son through Jake; Eywa would repay in kind by giving her one of her own children.
Sorry if it doesn't make sense but thank you for reading :D