Tumblr host their terms of service in a Git repo on Github.

https://github.com/tumblr/policy

Been interested in doing this too, but reconsidered since I don't know about property laws for EULAs/TOSs. But a public-facing TOS that tries to bind users and says "this document can change any time for any reason, and we will notify you by email, and it is your responsibility to keep up to date with it" should have some public domainness to it, even if it legally isn't: users should be able to "congregate publicly" to discuss their archived copies of TOSs.

(The counterargument of "don't use the service if you don't even agree with how the TOS is deployed" is technically agreeable but utterly impractical since "I am whimsical" clause in TOSs these days protects the vendor and not the user, and places 100% burden of trust on the user that the whimsical TOS will not arbitrarily screw you over later. Every vendor relies on the fact that there are so many other vendors out there, that some percent can eventually get a free ride on trust)

Suppose we provide the venue for congregation. How to ensure legal survivability?

I interned for an advertising aggregate - Evidon - and one of their projects is to monitor TOS for various advertising companies and show a diff. I wish it would catch on for everyone.

Like a changelog? I like it.