I know Microsoft has a forum similar to uservoice.com for feature and bug submissions, but it has slipped my mind and my google-fu is fail this afternoon. Then I thought... hey,
GitHub is the correct place to lodge these requests. Raise them as GitHub issues.
https://github.com/dotnet/csharplang
GitHub Issues:
Historical places not for current discussion:
There is also the Visual Studio Uservoice for requests pertaining to Visual Studio specifically
https://connect.microsoft.com/
Update: Connect has been retired. This GitHub repo is now the place to add suggestions.
Here is the official user voice channel for suggestions and ideas on the C# language.
Update: The UserVoice channel has been retired. This GitHub repo is now the place to add suggestions.