If a repo contains binary blobs, especially executables, well, that's very bad practices right there. Also, how can somebody else modify a binary in a meaningful way and send a patch to it? How can you review a patch to a binary file before applying? I'd say that any sane project, especially if open source, would not include binaries (maybe apart from images), and even if it did, would not accept patches to them (if the members of a project were talking about changing, say, an icon, valid images would be exchanged on a mailing list/issue tracker, nobody would bother making, sending and applying binary diffs; then somebody w/ commit bit just commit it).

Let me put it more simply: if you're accepting patches for binary files in your repos you don't care about security at all. Maybe unless if you know how to decode machine code/JPEG manually.

Also, the proposition was to use the full hash internally, and truncate the representation. Nobody other than git itself uses full hashes anyways.