This is a great idea--to add crochet motifs to an existing bra. I would leave the original cup in, because then you would end up with a crochet bathing suit top that wouldn't stretch and fall off when you wore it into the water!
How to Crochet * The perfect Bikini Top * Bustier for Summer Tops * for all Sizes This is genius! I am a size 42 F, and I never thought I would be able to find a pattern to fit, but this works for LITERALLY all sizes. And it's remarkable simple!