Years ago, I built a sort of camo-proxy like, in Elixir. It was doing full passthrough of the User-Agent because the project that I originally built it for needed it for the upstreams (i don't remember why). Anyway, I ended up pulling it into pleroma -- a couple of months later, we had been informed by some instance owners that google itself were sending them DMCA notices, because it was proxying googlebot's request, with its user-agent!