More open process could encourage adoption, ultimately improving IT project management across the industry. Organizations that have no experience with PMBOK or ITIL may not bother with it due to the expense and closed nature.
As I've been on projects with large schedule overruns, I am becoming more interested in the topic of project management to try to do better. However, ITIL and PMBOK seem way to heavy for what I need at a glance. My first approach is to simply look at following documented agile processes. What says that PMBOK and ITIL are the best options? In order to provide a FLOSS alternative, you'll need to build a community that really wants this stuff and can contribute the body of knowledge.