Doesn't simply requiring that all pull requests be squashed down to a single clean commit from a developer known to have signed the license agreements give you

Doesn't simply requiring that all pull requests be squashed down to a single clean commit from a developer known to have signed the license agreements give you back the exact scenario you have under SVN? Anecdotally, a lot of projects I've been involved with have required that pull requests be squashed to avoid polluting the "main" repo with irrelevant/undesired third-party history.