The tests pass in Django 1.3...?  My goal would be to support as much as is reasonable.  If Django EOL's something, then we can, but I'd say if we can support the older versions with simple fixes do it.

I used to work on a testing library that would run on every version of PHP 4 when PHPSpec would only run on the latest.  By targeting only the latest you hurt adoption from people who are migrating from/integrating with legacy code where a full-blown upgrade might not be possible.