Currently, the Breeze repository is just over half a gigabyte in size, which can take a while to download on slow internet connections. Most of the size comes from .git/objects/pack/. For comparison, the KWin repository has a lot more code and its earliest commits are from 1999, but it is only 10% the size of Breeze. I'm guessing all that space is taken up by history for non-text files such as PNGs.
I think it might be a good idea to separate the wallpapers, cursors and their history from the Breeze repository.