To be clear: I don't see CLJS ever removing whats currently available from the Closure Library, even if it did you'd just declare an extra dependency to get it back. So, if the thing is working there is no reason to ever stop using it. There are however very many things in the Closure Library that are a bit outdated and working around Browser issues that no longer exist, so there might be more modern things available that do the equivalent with less code.