I doubt Nothing OS based on Android 16 will have Material 3 expressive elements, as Material 3 expressive design will be released along with Android 16 QPR1 stable but Nothing OS 3 as far is based on stable Android 15 initial Release, so Nothing OS 4 or Nothing OS 3.5 will also be based on Android 16 initial stable release.
I just hope it has Mterial 3 Expressive elements.