I covered some of this in one of my previous blogs where i talked about the systemic challenges here that I've uncovered. The heavy users that I spoke to, 100% of them had a repository manager, some Nexus, others Artifactory. And yet the high levels of consumption still persisted. I discussed some of the reasons for this in the blog link below... but I think this refutes the theory that simply having yet another caching proxy solves the problem. It really doesn't. Additionally as Mike discussed, bandwidth is only part of the challenge. Without the people behind the repositories doing the malware response, the curation of namespaces etc, there wouldn't be anything to proxy anyway.
https://www.sonatype.com/blog/free-isnt-free-the-hidden-cost...