Recently I wanted to make a Kotlin version of my neovim-java library. Idea was to make it possible to use for any of available Kotlin targets, which will make it significantly harder to develop.
Check out progress at neovim-kotlin. Most of MsgPack support is ready in kotlinx-serialization-msgpack.
In the meantime I am also trying out Lua support in Neovim 0.5.0+ and I have also added vim plugins list.