Mullvad has been chopping away at system transparency for a little while: https://mullvad.net/en/blog/2019/6/3/system-transparency-fut... -- Effectively, a mechanism by which their servers can perform attestation to their server really being what is says it is.

I think they might have even spun this out into a separate project. With this, you can "trust" Mullvad that what's audited is really what you're using.