What's the new hotness that people are replacing it with?
Personally it was easy for me to switch from travis because all my CI scripts are actually bash scripts, so the .yml CI file is just a few lines pointing to those scripts. All I had to do with gitlab was make a base image to be the "CI image" with all the tooling necessary + docker-in-docker.
Upgrades to GoCD have been very predictable, in contrast to Jenkins :-)