This is true, but I don't know if simply making the potions drain would cause the game to enter "an uncanny valley." I mean, the potion draining doesn't bother me at all; I've hardly noticed it. But, a simple animation where the potion slowly vanishes as Link drinks it wouldn't be that time consuming or difficult, especially with some of the other things they did in the game. I'm certainly not saying that this is a flaw, or even something to get up in arms about. It wouldn't have hurt if they did it, and it doesn't hurt that they didn't.
Are you speaking from experience? Again, there are many things about game making, or any type of craft, that are actually complicated but seem easy to do. One can't assume that just because it seems simple that it is. Professionals artists draw grand pictures every day, but some of them still have trouble drawing hands.
Here's a more relatable example. The Jak and Daxter series is a game that is filled with all sorts of great animations. People flying on crafts, explosions happening, great facial gestures, etc. There is one scene in Jak 3 where Jak pulls down his scarf before kissing a girl. If you play the commentary during that scene, the animators tell you that the girl was actually supposed to be the one to pull Jak's scarf off of his face before they kissed, but having two characters make contact with an object inbetween them is a rather difficult thing to do in animation. Something as simple as making one character touch a scarf on another character is difficult to pull off despite all the what we would call "difficult" things that have been accomplished.
And I'm not saying that potion draining alone would make Zelda enter the "uncanny valley" (though I'm not saying that's completely impossible either). But once you fix potion draining, whats to stop you from doing adjusting with all the other minor not-to-real-life inconsistencies that Zelda has. Why is potion draining special? Since you've done that, might as well fix the Epona teleporting problem... and the fact that Link doesn't have an animation of actually picking up rupees... and the fact that Link's iron boots only work when he puts them on. Sure you might think that potion draining would be a nice touch up to the game, but the next Person feels just as strong about the next unrealistic trait. If all these traits are met, you've diverged from what was once a game to what is now a tedious task that is almost just like real life, but isn't exactly real life.
I think people are missing the point of my post. I'm not saying that potion draining is necessarily a hard task, it might not be. I'm not saying potion draining, or any minor detail, will make Zelda enter the uncanny valley, it may not. What I'm saying is that it is highly likely Nintendo has justifiable reasons not to worry about certain details like this. If potion draining is added, I don't think it'll be the end for the Zelda series, in fact, I'd probably love it. And there are plenty of games that do minor details which I highly appreciate and even think make the game that much better. All I'm saying is that game companies have worthy excuses for ignoring some little things, and in the case of potion draining, I'm not mad at them for doing so.