The point of having a Clang server (clangd) is to serve as infrastructure for "increasingly advanced and interactive C++ tools. It should generalize and build upon libclang, and will allow us to effectively target Vim, Emacs, and other editors."
Here's a longer description for the proposed Clang C++ services:
The overarching goal is to build support for running a persistent, caching service layer adjacent to a users' editor(s) of choice. This layer would provide much of the functionality that might traditionally be found in an IDE, but designed to work with different, very "unintegrated" editors and the widely used and popular command line development tools on unix-ish operating systems. It would be implemented in terms of Clang/LLVM's libraries to support C/C++/Obj-C/Obj-C++ development. It should be heavily integrated into existing Clang layers such as the Tooling library, libclang, and potentially the plugin architecture.This is currently a work-in-progress, but there's at least developers actively working on this project. Those interested in learning much more details at length about the Clang server, see this cfe-dev mailing list message.