I don't fully understand what you mean, please help me understand. Why would the generic term "code hosting" change to two brand names, and what does S3 have to do with all this?
By "code hosting" I mean that most places say "we support code hosting" but in reality their systems are only setup to work with/use github.com; the domain at the very least, and possibly the API on top of that. Now places are going to have to generalize a bit, at the very least by thinking of multiple domains.
There are undoubtedly going to be tiny differences between how gitlab handles things; those will surface over time. They probably won't make headlines, but they'll cause tiny localized headaches.
As for S3, I mean that the GitHub API (issue tracking, etc) is all non-git proprietary stuff. GitLab should copy that so people's workflows Just Work™. I have no idea if they've already done this, I'm sure they've considered it.
