No, 2.0 is not changing our support with GNU/Social. 2.0 is removing Mastodon-only OStatus extensions that have been replaced with ActivityPub. Mastodon currently has no plans to remove OStatus support for public posts or stop targeting GNU/Social compatibility as a goal of the porject.

Not quite. Version 2.0 will remove some OStatus extensions that we originally invented to circumvent the limitations of OStatus in regards to privacy. Traditional OStatus support will remain for the foreseeable future.