No no no no NO. It's time to get rid of Flash. Open-sourcing will make it live forever. Flash has very little to offer that is not at this point duplicated (or improved upon) by others. It's also woefully insecure. "Many eyes make all bugs shallow" will only work for the most trivial bugs in the most common code paths. Plenty of vulnerabilities will remain. In open source, they'll be even easier for attackers to find…
Even if it's not going to be in browsers, I wonder if there's value in open sourcing it so people can create applications that run flash apps. There's a lot of content out there made with flash, especially games.
A sandboxed player application would go a long way toward the uses mentioned in this thread, no? I wonder when we'll start seeing Flash emulators being developed to play back all that old content.