There were some proposals for how to improve the Bundle Editor and include a versioning and merging of Default bundles, local changes and SVN checkouts. I had wanted to whip something together (just a command line script which compares dates and makes diffs, to view and make patches), but did not find the time yet.
I also have something like this on my to-do, but you know time and priorities
I think a major weakness of tm at present is the need to use svn to get language features (bundles).
What I'd like to see for users like myself is a page which parses the SVN repository into a list of download links to current bundles.
This is how subethaedit works, and it is great for people who just want to grab a bundle and be done with it. (tm is better than subethaedit in that if you do get a .tmtheme or other file, tm can install it for you: subetha just says "you need to stick this in one of these places..."