In other words, you can build on this software in your proprietary software but can't change the Trailblazer source unless you're willing to contribute it back.

loophole: I wonder if this will actually just push people to move their code -- which at the core is/would be a direction modification to the source code - out to a separate module. That's so easy to do with Ruby, so this restriction hardly seems like it would have any effect on encouraging contributions.