Assuming that one day there will reproducible builds, how will they ever tell apart the legal use from the illegal use of the (bit-for-bit identical) binary?
By ensuring the proprietary builds are NOT the same.
Ouch! Then we have the choice between a community-provided binary that is cross-validated by multiple build servers of multiple distros, and a vendor-provided binary which is deliberately different and has legal restrictions. Which one would we consider to be more trustworthy?
Code signing maybe? Not entirely sure otherwise.
How would that work? The signature of the official binary would be also valid for the "other" binaries.
Code signing involves attaching a certificate from the author which nobody else can reproduce unless a CA is compromised. Think SSL certs to some degree. This only proves identity of person signing it. This would differentiate the binary enough I would think.
If the rest of the binary is bit-for-bit identical, you can just tack the signature on to the OSS binary.