alt Hacker NewsOne good case for it that I see is a viable basis for cross-platform desktop apps. Today, cross-platform desktop GUI apps are either just a snapshot of the website contained inside Electron, or a C/C++ code base with manual memory management. D can serve as a nice middle ground in that space.
Where is the extensive tooling support for this use case if that is where you think it fits?
Apple is all in on Swift, so you will not be writing native MacOS or iOS code for UI in D, best case you put your business logic in D but you can do that in any language which has bindings to swift/Obj-C.
Android is all in on Kotlin/Java, not D again
Microsoft is all in on C#, again not D.
Linux your two best options for UI is GTK and Qt, C and C++ respectively.
So the only place where you could bave seemless integration is Linux through FFI.
Here's the thing though, for building a core layer that you can wrap a UI around, Rust has insanely good ergonomics, with very good third-party libraries to automatically generate safe bindings to a decent amount of languages, at least all those listed above and WASM for web.
None of those uses cases are painless in D.