Anybody that ever worked on Hadoop could not sign such a pledge.
Anybody that ever worked on Linux could not sign such a pledge.
Anybody that ever worked on solr could never sign such a pledge.
And so on. You get the idea, it is not possible to contribute to open source projects that have applications in large scale data storage, mining, generalized operating system work and so on without as a side effect making the apparatus of mass surveillance possible.
The only safeguards that will really work are very strict legal ones, transparency and accountability. As long as the last two are not present the first is meaningless (which is the situation we are currently in).