FWIW, neovim's built-in LSP (nvim-lspconfig -- written in Lua, currently in beta) is _outstanding_ and I have already replaced coc.nvim with it in my neovim set up. Set up is super simple, there are 2 extensions to install. Configuration is simple, I think I needed maybe 8 lines added to my `init.vim`. With that I get completion and in-line diagnostics and it's very, very fast, at least with solargraph, clangd, and tsserver.