Semantic highlighting is finally in preview as of VS Code 1.42.0. C# is an ideal candidate for taking advantage of this feature, as the available TextMate grammar is pretty lacking, and the syntax of C# is such that it's impossible to accurately classify many tokens with a simple line-by-line regex parser.

• SemanticTokensProvider API (proposed)
• Basic extension sample
• VS Code's implementation of semantic tokens for JavaScript

I'd love to help out with this, but I'm not at all familiar with the codebase here. If this is a feature you would like to support, I'd be more than happy to open a PR if someone would be willing to provide some guidance or a push in the right direction.