Number of failed tests sounds like a great idea to me. Still, it is problematic that we get a "failure" notice every morning when all we have are known issues, it means that nobody cares what's in those tests anymore.

I would simply change the email title to "results" :-) Given that there are a bunch of separate modules in there maintained by different people, I don't think it makes sense to aim for a state where a single bit provides useful information about all of IMP.