Why make this such a limited set of options? Why not let me enter a path, for example, instead of hardcoding "/docs"? What if I want to serve my docs from a stable release branch or tag instead of "master"?
1. The overwhelming majority of users use one of those three design patterns. For example, I can tell you that more than 98% of GitHub Pages sites use either `master` or `gh-pages` as their primary branch (with only about one tenth of one percent of sites using the `stable` branch).
2. Our experience tells us that every option we add to GitHub Pages increases the learning curve for newer developers. With only those three options, if you're just learning HTML, you don't need to understand Git's branching model before you can create your first website.
We chose these options to start because we thought they struck a good balance between supporting collaborative documentation workflows for open source projects and encouraging "hello world" experimentation among new developers, but as with most features at GitHub, this is just the start.
You have two choices to make: which branch and which path within that branch. The defaults are "master" and "docs," but allowing maintainers to make different choices there doesn't need to impact the onboarding experience for new developers. The newbies use the defaults - people who need customization can customize. Software development is a broad field and projects work within various constraints and architectures. Asserting a convention here feels a bit misguided.
You already allow the default branch to be customized. It's a bit weird that I can specify a default branch (like "develop") and delete the master branch, but then won't be able to publish docs without recreating master or maintaining a gh-pages branch.
Expecting GitHub to spend real money to cater to a tiny minority of users of their web service is misguided. The business models behind public internet services are simply not structured to cater to anything but the lowest/simplest common denominator users.
It's great to see new features shipping on GitHub.com (especially since it felt stagnant for so long). I have no idea what their codebase looks like, but prepopulating a text field with the contents of a template.md file and allowing the name of the publishing branch to be specified feel like they should have been fairly minor changes. Especially now that they clearly have the architecture to choose repo-specific publishing locations, allowing those to be user-specified should be a very low-effort way to make the tools useful for more projects.
You must be new here...
$ git subtree push --prefix=public origin gh-pages