Admittedly I'm not in the inner circle, but this is the first time I've heard the idea. It's certainly intriguing. In this case would the one-to-one branch include the full SVN repository history (all projects), or would svn-fe/git-fast-import filter down to subdirectories of interest?
Along those lines I can contribute the following data point: my initial fast-import repository weighs in at 1.3G, while after my scripts run the final product is 659M (and no, they are not hard linking to each other). Unfortunately I don't have a good accounting of the size difference (obviously some is filtering down to a single SVN project).