this is the developer of highlight (without GNU prefix, see http://andre-simon.de), the other universal syntax highlighter you probably know ;)
As both utilities have a very similar use case, they already share some command line options. My suggestion is to enhance both apps' interfaces and docs to offer the same long options for (basic) highlighting. Third party apps like webgit or viewcvs could implement plug-ins which work with gnu-highlight or highlight, no matter which app is installed.
I only intend to harmonize the CLI, not the language definitions, C APIs or other internal stuff.
Options already shared: