Unless the protocol changes to specifically address this, I find it unlikely that LSP will ever be a full solution for real-time syntax highlighting. The amount of JSON that has to be slung interprocess on each edit is just too much. Providing extra semantic highlighting on top of a built in option, absolutely, but I don't think it can replace an in-process, specifically incremental option like Tree-sitter or Sublime/TextMate language defs (or a completely custom solution like JetBrains, Nova, etc.).