(Speaking for myself.)
I don’t see why chain forks should be treated differently to code forks, to be honest. I don’t think that the example of ZClassic is pertinent — there are other code forks (such as Pirate Chain, for example) whose devs have as far as I can tell always behaved ethically, and I’m glad that those chains exist.
As @GGuy points out below, projects that are technically chain forks can be effectively code forks, so I don’t think that this distinction is legally enforceable anyway.
“Any project related to Zcash” is indeed more like the exception that I thought we’d get; the narrowness of the current exceptions surprised me. (Note, however, that it still falls foul of sections 6 and/or 8 of the Open Source Definition, and it doesn’t solve all of the license compatibility issues. Combining a broader exception with dual BOSL/GPLv3 licensing would help.) I respectfully disagree with Zooko’s opinion that this “isn’t currently a big deal”; in fact it seems to be central to the arguments of some critics of the use of BOSL.
I wish that the BOSL licensing had gone through an engineering review process by Core team, and I think that if it had then most of the problems that have been raised would have been avoided.