Mosh is really awesome. But I disagree with "tmux is the new [GNU] screen". That's like "clang/LLVM is the new GCC". It might have some new features which you might need (such as the LLVM infrastructure, or for tmux the vertical window split which is preserved during detaching), but for many use cases the "old" software is still fine. For the presented one here, GNU screen does exactly the same fine job as tmux can do.