Update...Sadly, this adorable chick didnt make it. We had a cockerel that was attacking chicks and this poor thing wasn't as lucky as the other one I managed to save.
However, shortly after this post, we had a broody Maran hatch chicks and a couple of them also have leg feathering. The only common denominator with the chick in the post and these maran cross chicks, is the Welsummer rooster we recently had to rehome. He was dad to the chick in the post and is grandad to these feathered leg chicks. Is it safe to assume that this trait most likely came from him? I didn't think Welsummers had feathered legs though