¤ Yeah I'll have to agree with Aaron here, I don't feel like the babies dying of separation anxiety when they are separated from their parents yet are still within earshot of them is a bug that should be fixed (at least not in the Community Patch you mentioned Hiracho), it really feels like it fits the BTW theme. I'd agree though that babies dying because their AI still acts as if they can jump 1 high block is something that should be fixed.
¤ I'll admit that I totally blanked on the grass conveyor thing, that's a pretty cool concept that I'm looking forward to play with ^^
Although I still managed to figure out how to breed all animals using large pens and water, the cost of doing so was really high and full of little annoyances, except for chicken :
With a pen that size :
(so 5x7 inside the walls, or 7x9 including the walls) and a wall dividing the middle, you reach a perfectly balanced point between the amount of grass eaten by a chicken/the grass dying under water, the growth rate of grass and the time needed to collect the eggs with water (16sec max, perfect for a turntable timer)
Some side views :
And if you move the water channel and the piston a bit further back, you can actually stack them, making it only use one piston and increasing the grass growth rate :
(you can even move the top pen 1 block lower)
In my last 3 playthrough I actually built one of these as soon as I reached the nether, and so far I've yet to see them fail.
A few more pics from my current world :
Overall they work very well and are pretty cheap to build, and the only slightly complicated part isn't actually the pen, but counting to 4 for the decay timer to feed them every day :D
¤ Now where it gets hard is for bigger animals, and since cows are the ones that require the most food and space, I went for it to see if it was doable. And it is, but oh boy is it a massive endeavor. I don't have access to the old worlds I built it on at the moment, but I still have a few pics available so that'll have to do for now :
Here the basic proof-of-concept built in creative :
The cows spend their days on the top part above the green wool (#2 on the pic) the whole thing is 60 blocks long, and iirc they were 28 blocks large.
Once a day water would drop from both sides and the middle to carry the cows into two water channel (the drop above said channels was blocked during the day with pistons, so the entire field was available for the cows), and the cows would end up in #3; where they are fed cake, separated from their offspring based on size, and sent back up to their pen using the elevator in #4, going back to #1 ; while the babies would be sent far away to mature before evolving into meat and leather.
I did end up building one in survival
but given 1) the absurdly ridiculous cost of time and materials required for such a low yield (the pen could hold safely a maximum 6 cows, so that's 3 cows per day max)
2) all the little annoyances, like cake recipe not being 'automatable' (I think ?), cakes not stacking, and not being able to use the increased inventory of the BD to store more (BDs can't spit out cake, they'll try to place it as a block), meaning you're stuck with using a regular dispenser + a non-full hopper on top
and worse of all 3) barely a day after I finished building it, an enderman teleported in the pen (the pen had to be 3 high at the spot where the water drop down), stole some grass and broke the whole thing ...
In the end I don't think I'd advise for building anything similar in the current BTW.
Sure, the enderman thing is avoidable (just make the whole pen on the same y=lvl, just longer) and completely random (it never happened again in the hundreds of days I played after), but the cost is so prohibitive, I believe that the conveyor grass idea is the right way to go :)
It did look fucking cool though :D