Hi, I am a user of subgit (through bitbucket).
One of the great features of subgit is that it is not limited to immediate migration but can support an indefinitely long transition period where the repository can be used with both svn and git clients side by side.
This does not work, however, with git submodules.
I am not asking for subgit to automatically convert svn externals to submodules - just for it to be capable of representing submodules within the source svn repository. The .gitmodules file can be stored as a regular file but the “commit” object cannot. I suggest representing it as an empty directory in svn with a custom property containing the commit hash. It could also have an svn externals property, of course.
Another feature that might help is in the opposite direction: something that can be represented in svn but not in git. I am referring to empty directories. Build scripts will often fail because output directories are missing. While this is trivial to fix later, it hurts the first-time experience of “wow, it just works”. This can be implemented by placing an empty .gitignore file in the git representation of empty svn directories. This should be an optional checkbox, off by default.