I love
Rosie as a nn or a full name actually. Personally I wouldn't hesitate to use it as a full name. I think if you want a full name for the nn
Rosie, then
Rose "
Rosie" or
Rosemary "
Rosie" are your best bets. I don't know that it will gain in popularity hugely.
Rose is such a common mn, that I think people will continue to use it in that place.