Regional spellcheck will be available. We have an issue logged for it https://github.com/brave/brave-browser/issues/726
This is not the case and never will be. There is a lot that goes into Chrome that is propretiary to Google and Brave doesn’t do the same. You can read about the difference here.
Regarding Private windows this is currently done so as to isolate the data that gets created on the profile when using the same window. Its not that Private tabs in same window is abandoned. Its still on the roadmap and you can read whats coming ahead in the Brave Roadmap
Thanks for the feedback.