Interesting that they're going this way.
We used Google's source repository functionality for a while because there is no real choice if you want to use Google Cloud Builder, which we were testing out for cloud-based Docker builds. GCB was pretty disappointing, and we moved off it.
We also found the source repository service annoying. GCB can't pull code from Github, so you first have to set up a Google source repo and turn on Github sync; the source repo is, in other words, only there to be a mirror. Unfortunately, this introduces problems. You get latency -- your Google repo is always behind. Worse, we frequently experienced a situation where the sync was broken, either due to Github being flaky, or the syncing itself being flaky. In such cases, it was impossible to tell what the status of the sync was; all you could do was go into the UI and see that it was not up to date; no way to force a sync. So this setup became a liability. At the time (not sure if this is still the case), there was also no API to set up new mirrors, it was all manual. The whole UI around GCB and source repos seemed to have been created in a rush, very bare bones. A lot of Google serviced start out like this.
I suppose this is a strategic play. For developers, you'd get a better UX if Google simply had tighter integration with Github and Gitlab, but Google probably doesn't want that. However, the low quality of their offerings so far (especially, cough, StackDriver) mean that this stuff will have an uphill battle in proving itself to developers, most of whom already have an allegiance to better tools like Github. If you're already on Github, why would you use this stuff?
