We supported Mono in the past and will again in the future. Currently Mono support is disabled merely as a way to focus our limited resources as Mono requires a different set of plugs.
Development has also started on using .NET Core, which is a cross-platform version of the .NET framework, and although Visual Studio is a Windows-only application at the time being, using Visual Studio Code (a cross-platform Visual Studio IDE) may be a possibility in the future.