First things first. This is a trade good of massive proportions. Not quite on the level of salt, but there is a reason France has been known for centuries for its wines.
Yes we could use the stability or the boats, but neither is such a valuable long term investment. It is also another farming and gardening technique. This is the chief belief of the people. Lets act on it. We have seen how easy it is to lose abilities. Furthermore, any and all agricultural techs are like gold in our hands due to compounding effects of all our other agricultural abilities.
EDIT: People have stated later in the thread that this would likely improve our 'Improve Festival' actions. Probably likely.
[X] Develop vineyard (-1 Econ, +???)
The cow is a bit of a weird consideration, and my first thought is that it is an albino and therefore at risk of a whole host of genetic issues. However, there is also this:
The Belgian Blue which is a breed of cow that is sometimes pure white. More importantly, they have genetic hyperplasia and their muscles grow 'lolhuge.' Im going to say we should breed it, but maybe someone else can chime in.
[X] Breed it
I would love to kick the hathatyn out of soputhshore. However, I'm super leery of more war actions and the nomads hitting us while we are kicking them out. We need to spend some econ here, so I'm going to say that we should just spend it on more boats. Other effects are nice, and so is the extra diplo, which yields art. I also wan't to try and dial back on the warrior focus we have been building up of late. It has caused nothing but trouble for our historical enemies and we should avoid it ourselves.
[X] Build boats to counter them (-2 Econ, +1 Econ and +1 Diplo next turn, other potential effects)
Last but not least:
Chinampas I'm a little leery of letting step farming go as it comes with a whole host of other technologies related to earthworks. By the same token, this is pretty valuable, especially once we build the Dam and get some larger lakes. For now, I think we should just take it in the spirit it was given. The Dead priests are basically done as an independent civ, and the wider Thunder Horse are unlikely to need/use such techniques.
[X] Yes (Trade step farming for chinampas)