It looks like Travis has a "pro" edition coming, but the link goes to a placeholder page ATM
I think there is an aspect which I didn't mention of "Who do you trust with your code?" and GitHub has done well to earn the trust of lots of great companies, but I can certainly see IT managers getting a bit ancy at adding another point of confidentiality failure by looping in Travis as well.
Though the same users that want such a thing are likely also running (locally hosted) GitHub Enterprise, it'd make more sense to provide a similar option for Travis.
If you're interested, you're more than welcome to get in touch with us (mathias@travis-ci.com).
Mathias/Travis CI