Neovim and VS Code are very popular because it is easy to create a plugin and integrate it with everything. It's true that Kate has a native LSP configuration but it is missing as example the linter support on save as example and many other things. Looking at my experience with browser extension maybe let to develop plugins in Python or other solutions can simplify the extendability of Kate.
Closing as out of scope. Its difficult to make a system that is truly extendable and also easy to use. The current way to develop plugins is simple enough, it just requires that you know C++ and our APIs. We have a javascript scripting system, try to use that. If you need to do a specific thing, then open a bug for that thing.