I thoroughly agree with this argument, and have raised essentially the same point internally at ECC. I’d like to state publically (speaking only for myself) that I believe this is a really important argument for using a well-established, permissive license. In particular it was used to argue for the relicensing of the halo2 repo as MIT, and I don’t personally see why it shouldn’t apply equally to the orchard repo.
To clarify, my position is “MIT, or (BOSL/GPLv3 plus a broader exception that allows both permissionless forks and any Zcash-related use)”. If the non-MIT route is taken then I would also prefer that any fork exception not make a distinction between chain and code forks.