Having the .travis.yml file in the repository does not enable Travis: you have to enable it on travis-ci.org UI. So it won't make any noise except if we decide it.

What we gain is that people forking the repository can have CI for their forks by enabling Travis there. Might be handy to run CI while working on your branch (and before submitting the PR).

I personally would like to have it especially when working on long term work.

That being said, at one point, it might be a good idea to switch to Travis anyway for PR validation as it has a lot of traction in the Open Source world (so people are used to it). But it's another discussion and I don't think we're ready yet (at least on the Validator front).