I did some contract work some years back with a company who had a desktop product (for Mac) that would apply some smarts to strip out extraneous things on pages while printing (such as ads on webpages) as well as try to avoid the case where only a line or two was printed on a page, wasting paper. It initially was getting into things at the PostScript layer, which unsurprisingly was horrifying, but eventually worked on PDFs. This required finding and interpreting various textual parts of the passed documents and was a pretty big technical challenge.
While I'm not convinced it was viable at the business level, it feels like something platform/OS companies could focus on to have a measurable environmental and cost overhead impact.