Modern systems language?

(Spoiler: There isn't one)

C and Sepples are more trouble than they're worth. Pascal is basically a better-and-yet-somehow-worse version of C. Ada is basically a better-and-yet-many-times-more-verbose version of C++.

I don't think I need to say what C++ is.

Go will never be good. Python will never be good.

Is there a language that's good that I don't know about?

C is what one would use for system's programming in modern OSes, simply because it is a low level language, has a tiny runtime, and compilers are good for it.
If you want something which makes programming less boring/redundant, you could go with some low-level Lisp of your making. This worked quite nicely many years ago, and would work even better now that we have faster systems, however it's easy to write slow code in Lisp if you don't pay attention, so expect to spend time profiling and writing optimizers for your compiler to achieve decent performance. I can't consider Lisp for system programming on modern *nix'es or Windows since that would mean having to load some 2-40mb of runtime just for a driver, which is overkill for anything, but an operating system. I haven't even considered what redesign of the package system would be required to implement some proper multi-user security subsystem, if Lisp is used.