If WordPress won on the trademark infringement issue, it would be a fundamental rewriting of trademark law as it exists in the U.S. today.

Companies even competitors are allowed to use trademarks when they are making factual statements, like "we provide Wordpress hosting" as long as they make it clear that they are not the trademark holder (i.e., confusing customers). Even before they revamped their website, WP Engine was very clear about being a third party provider for hosting WordPress blogs. They weren't claiming to be the original WordPress, or the original WordPress hosting provider, or anything similar.