This is something I've yet to see a software testing framework do. Compare the results of two different implementations separated in time. i.e. two different revisions out of source control, using one as the golden reference for the other.

bazhenov/tango does something like this for performance tests, basically to counter system behaviour you run the old and new implementation at the same time.

Isn’t that kind of what snapshot tests can do?

I maintained a fairly successful legacy C/C++ application that performed business critical functions. The core developers were long gone, and countless of changes had to gone into it since. The only way the application survived was automatically comparing outputs and intermediate data structures against "ideal" values. Hundreds of business scenarios with their own input datasets. No one really understood what each scenario or ideal value meant. So your goal was to minimize divergence, and update the test case if it was deemed acceptable.