Yeah basically. It was originally removed because of a now patched denial of service vector, but you can do eltoo, covenents, and kinds of stuff with just op_cat. Even the block stream article I was reading about op_cat schnorr tricks said it needed deeper review due to what its capable of.
I like the check template verify (CTV) style of BIP better
If it's too generic I can imagine it'd be difficult to preclude DoS attacks aren't possible. I guess we'd have to be suspicious of operations where the computational cost isn't proportional to the operation's size, but I don't know enough about bitcoin script to imagine OP_CAT breaking that.
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