There would be more features with the final release of programming language C# 7.1 in addition to previous, following are the features that encountered a bug or partially implemented as on date.
The pattern-matching with generic is proposed here: https://github.com/dotnet/csharplang/blob/master/proposals/generics-pattern-match.md as new feature of C# 7.1 that encountered a bug and can be seen here: https://github.com/dotnet/roslyn/issues/16195
The implementation of this feature would be based on as
operator as detailed here: https://github.com/dotnet/csharplang/blob/master/spec/expressions.md#the-as-operator
Reference assemblies feature is yet to be incorporated within IDE, you can refer: https://github.com/dotnet/roslyn/blob/master/docs/features/refout.md here for more details.