Just what did Toady change about the game?
I missed it.
Well, people like to say that after this thread the creatures that [CAN_LEARN] were made unbutcherable (with dwarven ethics) and mermaid raws no longer had value multiplier. (Elves, gobbos and humans could butchered back then as well, and in a fact dwarves did that automatically. Actually goblin bone crafts comprised the majority of non-rock trade goods. It's just that their value was rather low, so they never got that much attention.)
However the next version after this thread was huge release of .31.01 which was almost new game. The entire way of how creatures were represented in game has changed and the most of the tags responsible for mermaid phenomena became obsolete.
So, to me it seems that mermaid price was lost\revised in the process of complete re-factoring of raws. And the inability of butchering sentients was just a result of development of entity system. Unless someone has a quote of Toady on the mermaid business.
But nevertheless, mermaids don't have anything interesting about them anymore, the most effective means of capturing oceanic creatures were developed in whale-hunting thread and new morality horizons were reached since then in other well-known threads. Thus this thread has now only a historical value and belongs to the archive aka pages that aren't first. It's not like they get erased around here.