I'm not convinced we should include EGit and or JGit into the Eclipse SDK. As a developer of the Platform for many years I rarely "start from scratch" in setting up my Eclipse installation for Eclipse project development. But when I do I simply install the EPP that includes PDE and EGit already and then I configure p2 to get updates from the Eclipse project I-Build site as well (
https://download.eclipse.org/eclipse/updates/I-builds/). Then I can simply check for updates regularly to pick up the latest I-Build. I do not find this all that inconvenient. Additionally, as a committer to the project, it gets more testing of what we deliver to make sure it is upgradable so we can catch issues earlier that may block our users from updating from one release to the next. On the other hand, adding another outside dependency to the Eclipse SDK build will force another project to adhere to the platform +0 schedule. That may not be acceptable for the EGit/JGit project.
For a lower barrier to entry for contributors, I do not think it is essential that such contributors use the very latest I-Build to contribute. They can use the last stable released EPP that includes PDE and EGit to do that.