As far as I’m aware, the only OneD&D mechanic in the game is the +2/+1 floating attributes, and that’s already in 5th edition via Tasha.
Other changes to races and spell lists are not going to be implemented in BG3. Mark my words.
The suggestion that WotC canceled its projects in this way doesn’t make sense. They hold the license. There is no contractual reason any projects couldn’t just switch which ruleset they are using if that’s what WotC wanted.
