The current bug reported here (https://fogbugz.unity3d.com/default.asp?807081_p6p8jtakhuvskj2s) was closed, but I did not see an open Feedback request on the issue. As an engineer working on service integration, being able to have QA & client engineers use proxy services like CharlesProxy is critical for quick turn around of bugs in our server configuration / services connections (e.g. header response configuration issues during migrations for WebGL builds). Since UnityWebRequests are pitched as a replacement for WWW requests, there is a developer expectation that proxy support will be integrated with this new model.
Please let me know if I am missing docs on how / when this will be integrated.