BIP 118's Motivation section says:
“Possible alternative approaches would be to define new script
opcodes, to use a different taproot leaf version, or to use a
different set of SegWit outputs … however all of these
approaches are more complicated, and are better reserved for
other upgrades where the additional flexibility is actually needed.”
What specifically made opcode-level alternatives (e.g. a hypothetical
OP_CHECKSIG_ANYPREVOUT) more complicated than the chosen pubkey-type
approach? Was it spec effort, implementation effort, or consensus
surface area?
I'm asking because, in light of recent CSFS (BIP 348) and CAT
(BIP 347) discussions, the opcode path now seems tractable. Curious
how the original trade-off was reasoned at the time.
