One of the first animations I ever did was a
foot growth animation. It was only an experiment in the whole thing and the only thing you see IS the foot and a bit of the leg, but eh, I figure it somewhat fits the topic.
Though I'm not entirely partial to the growth of just the feet, it's just because I haven't tried it myself really. After all, if I can be into selective shrinking where the legs end up not shrinking making them huge/ultra long looking, I don't see how just the feet growing would be much different.