> Re-enabling OP_CAT with the exact same OP would be a hardfork, but creating a new OP_CAT2 that does the same would be a softfork.

We have TapScript for that. OP_CAT is defined as OP_SUCCESS, it can be re-enabled in a soft-fork way. For now, OP_CAT in TapScript simply means "anyone can move those coins", so adding some restrictions is all we need to re-enable this opcode. Introducing OP_CAT2 is not needed at all, unless it will be totally different, but then it should not be named as OP_CAT2, but rather as OP_SOMETHING_ELSE, it depends how different it will be from OP_CAT.