I think it would be great. I am a mother and a godmother. However, there are plenty women who are asked to be a godmother who do not have children of their own. The group would allow those who have that in common to discuss and get advice on different topics that only a mother would know.
Have you done a group search to see if one already exists? If one doesn't, start your own. You'll have to probably write daily journal entries about it to publice it though, seeing as you can't tell who is a godmother from their profile.
Also I agree with you, the first response you recieved was rude.