The problem is not a lack of syntax highlighting per se, but the inconsistency of existing syntax highlighting. This is especially annoying in Common Lisp due to the existence of symbol macros, where syntax highlighting would be immensely helpful. I get that there are issues with symbol manipulation, but AFAIK language servers already evaluate code, even if not for syntax highlighting. I view this whole thing as an issue caused by the REPL workflow, not the inverse. Not to say that I would be willing to give up said workflow but it could certainly use improvements.