From the experts:
Etta, once a short form of Henrietta, has long been used on its own, and we wonder if it could follow the progression of Emma to Ella to...Etta.
Etta has taken the first step, having recently been picked by a celeb, Carson Daly, said to have been inspired by the late great soul singer Etta James, just as previous parents were similarly influenced by Ella Fitzgerald. Etta was born as a shortening of names with that ending —in fact Etta James's birth certificate name was Jamesetta.
Etta was a Top 100 name in the last decades of the 1800's, then slid down until it fell off the list completely in 1966. But with its delicate sound that also has a bit of crackle, and its new starbaby status, we can see this as a likely successor to the currently favored 'E'-names. Henrietta "Etta" Bishop was a character on the TV show Fringe.