Britney Spears - Of course... I think she'll keep going even if JUST to reach the landmark.
GaGa - I honestly don't think so. Although maybe she'd just keep releasing duds for the sake of being able to say she released 10 albums.
Rihanna - Easily. She'll be there in a few more years for sure. She may even reach it before releasing a GH album
Jennifer Lopez - She's so close now, so she's bound to do it one day.
Beyonce... I'm really not sure. She takes longer to come up with good albums than the rest of the girls, and I think maybe 4's relative under-performance may encourage her to take more time with the next album. Plus, she's starting a family now... I think album #5 may be a long way off.