I find nemo-media-columns as essential as e.g. nemo-audio-tab (already in repo) and it would be nice, if it gets added to the extra repo too.
I think all of the extension listed here GitHub - linuxmint/nemo-extensions: A set of extensions for Nemo should be available in the official repos, because they are part of the nemo eco system.
I prefer nemo would have these functions build in, but this won’t happen soon I think.