I don't think most would consider Molly O'Day (d. 1987) a bluegrass singer. A deeply traditional country artist, yes, but a disciple of Bill Monroe, no.
As a music reviewer at the receiving end of a fair number of current releases, I can attest that there is no shortage of current bluegrass far poppier than what Rhonda Vincent and Alison Krauss (at least when she's with her BG band Union Station) put out.
At the moment I'm finishing up a review of the new Laurie Lewis disc for Rambles.Net. Great stuff, in terms of both performance and material.
Lewis and her occasional musical partner Kathy Kallick are the Hazel & Alice of our time.