Travis CI is pretty minor player (google search 10M > hits), and I would say 3rd party service integration is exactly vendor lockin.
Imho this makes sense, because users who cared about pricing already moved on to cheaper alternatives and/or not used github to begin with. I agree, mass migration or phasing out github is unlikely because of the associated costs, however with all the other great services around new users might think twice where to sign up.
