Pixie maintainer / OP here. There's a lot of debate right now about licensing in the open source community. We made the call to go with Apache 2.0, and the lead of our project wrote in the post about why we made that decision.
Pixie will remain licensed under Apache 2.0. We are also working on moving Pixie over to the CNCF, to maintain this guarantee. This is being tracked here: https://github.com/cncf/toc/issues/651
In addition, we will likely move to a DCO (Developer Certificate of Origin). We are still trying to figure out the exact logistics, but this will allow commits to happen without signing a CLA.
> We agree to license the Contribution only under the terms of the license or licenses which We are using on the Submission Date for the Material