I worked at Adobe near the Flash team back in the day, and the PMs I knew would have absolutely loved to open-source the Player. The problem isn't willingness,

I worked at Adobe near the Flash team back in the day, and the PMs I knew would have absolutely loved to open-source the Player. The problem isn't willingness, it's third-party code, of which there is apparently a lot. If there was just a button to be pressed, Adobe would have pressed it circa 2010. But at this point, I think open-sourcing Flash Player is the kind of thing where the project to figure out what all would need to be done would cost more than Adobe would want to invest, never mind actually doing the necessary work (both engineering and legal).