Consider me part of the crowd that is very interested. Travis is atrociously bad. Jenkins I've heard some good things about but I have mostly negative experiences with it. Alternatives are needed. And something like gitlab would sorely lack if it didn't have CI integration.
We do run Jenkins currently for some projects, but nobody is really happy with it. Sure, it gets the job done, but not the easiest software to work with.
The advantage being that you can use the same scripts during development.
* General awfulness when it comes to packages. Outdated packages. Nonstandard packages. Ubuntu, instead of debian + testing, is a terrible choice for a CI.
* Horrible support for multilingual builds. God forbid if you have Python 3 scripts in your go project.
* With github, force-pushing during a build causes the build to error and travis can't detect that
* Lots of papercut issues in the UI
* There's always something when setting it up on a project that makes me end up fighting with it and figuring out crazy workarounds for it for several hours.
There's a lot more, though most of them have to do with point #1 and their choice of Ubuntu as a platform. I don't remember the rest.
Ok, fine, bugs exists in software. I emailed them saying that 'Guys, you should email only repo owner when payment fails, no everyone on the team". No response. I considered that lack of support and moved to circleci.
I have not. It doesn't look to be open source though, so not self-hostable - my interest stops at that point.
Until it gets basic features like that, Jenkins it is.