It might be worthwhile to check out Perforce [1]. Downsides: proprietary, expensive. Upside: you can version all sorts of content at a high level, not just software. I know of a large embedded shop that swears by Perforce.
However, it's worth considering if subversion is actually what you need (I haven't used Perforce but I have heard its underlying structure is conceptually similar?) I saw sysadmins struggling with Git when all they needed was to enforce good use of a single branch, and central repository and some history. They felt they should be using Git, and in doing so threw away a tool that was already a good match to their workflow.