Your comments
It might be too late now but why not do this in multiple steps:
1. Build a VCS plugin framework
2. Create the GIT plugin and open source it. Shouldn't that get around the licensing issues? The plugin is essentially free (provide it as an "in app purchase" for free).
3. Create plugins for other source repositories.
Customer support service by UserEcho
Any updates on this? There must be a way to implement git, there are several commercial GUI git app clients so this whole conversation around GPL and requiring a command line is not true and quite frustrating. Maybe the libraries you've looked at require that so find another way to integrate. If cost is the problem, then make Git, SVN, Mercurial in-app purchases. I'd be willing to pay another $3-5 for these features.
Stop making excuses and build it already.