There is a more up-to-date version of the highlighter included in snakemake itself:
https://github.com/snakemake/snakemake/tree/278beaa7c81b9e418fa42ac5f944e3d7e2cdfbbd/misc/vim
A difference, for instance, is that it colors the "best practices" suggested extension .smk, or that it does not break highlighting if there are numbers in rule names.
If this is not actively maintained, does it make sense to link to upstream's highlighter instead?