I vote for promoting "get bundle" to a normal part of the application, a major and clearly marked feature, not an adjunct plugin.
Getting bundles of functionality is not merely a "nice thing" in TextMate. It is the very essence of TextMate. The process of retrieving and managing bundles should be an absolute first class experience. I'd say my ideal would be something like Quicksilver's plugin system.
Short of actually editing text, managing plugins is the most important thing I do with the app.
I think *distribution* should have absolutely nothing to do with version control, under the assumption that whatever system is selected, it presumes the user will have it present on their system.
Of course, this is all moot re: how developers manage code for their plugins. Having considered this situation at my own company, the benefits of distributed source control are transparently obvious to me.
But that should be orthogonal to distribution to users. I really hate the whole "let's just do an svn checkout to get stuff" concept, and I understand perfectly how to do it.
-andre