This might be one of the rare times it's worth it. The C# team alread has the experience and tooling to maintain a language. Maintaining a DSL might be a reasonable choice for them.
It's rarely a good idea for app or library devs to make a similar decision.
Yes, this reminds me of meta-programming in languages like Python, it's useful if you want to create a framework like Django, but if you work on products, chances are good you should not use it.
This might be one of the rare times it's worth it. The C# team alread has the experience and tooling to maintain a language. Maintaining a DSL might be a reasonable choice for them.
It's rarely a good idea for app or library devs to make a similar decision.