I think B&N are clearing out the back stock. You might think I'm just rambling on, but I want to remind you that Engadget heard just this rumor back in January. I think it's now coming true.
The really interesting part is that the Nook Wifi isn't on clearance. That suggests that it's not going away, which means B&N could plan to keep it as a budget model.
If the Nook Wifi does stay then that would probably preclude a Mirasol screen ereader (I didn't think it was likely). B&N probably won't want to have to explain too many screens to customers. So I'd bet the new -reader will have an E-ink screen.