So, full disclosure, I helped create and ran the developer tools group at a large, well-known tech company. This is a space I'm intimately familiar with.
The idea seems pretty straightforward to me and not particularly insightful. Calling it an OS is different from calling it a platform, but effectively it's the same thing. Perhaps more interesting are the implications of that analogy -- do you ship APIs and have a lot of third party people building on top of you like in the Github model or do you go more in the direction of Atlassian? I know that's a bit of a false dichotomy, Atlassian has APIs and Github is clearly trying to extend their toolchain, but in general you have one with a rich ecosystem and the other where you mostly ship what they provide.
For myself, I see GitLab trying to be more of a Github alternative than an Atlassian alternative. I don't know if that's your strategic intent, but that's how it comes across to me. In either case, I think the industry in this space is pretty unexciting in terms of the kinds of innovation that are happening right now. Google still has a toolchain that is a decade ahead of most of us, and I don't see anyone really tackling that head on.