Given the ubiquity of tech debt in Unity I could see Apple maintaining support for the current C# version for the time being and in the long term, replacing it

Given the ubiquity of tech debt in Unity I could see Apple maintaining support for the current C# version for the time being and in the long term, replacing it with a full rewrite based around Swift with a temporary C# compatibility layer to pull the ecosystem through the migration, which wouldn't be everybody's cup of tea but could be interesting.