I agree but at least some of the ecosystem concerns can be mitigated if you choose the right technologies to build your language. For example Eclipse Xtext lets

I agree but at least some of the ecosystem concerns can be mitigated if you choose the right technologies to build your language. For example Eclipse Xtext lets you design languages that can easily interact with Java code and tooling, and it provides a lot tooling support like build integration in the IDE, syntax highlighting and code completions without much effort. If you keep the scope of the language small and treat it like any other module in your projects than its not hard to maintain.