I can see it coming back for girls, albeit not to the extent of its peak popularity in the 20s and 30s. As another user said, it did rise a bit last year. It's also a -ley name, and I could see it being used by parents who want a -ley name but want to go with something a little more conservative.
For boys, I don't see it ever coming back.
Shirley's firmly within female territory. TBH, I can't even picture it on a boy.