It's already in production from a variety of manufacturers in China. At the moment, though, it's really hard to find and I'm not sure what pixel densities they've achieved. The person who knows which suppliers might have transflective panels is Nicolas Charbonnier (AKA Charbax) from Armdevices.net. He has been calling for transflective technology to be used in a device for years now. His Twitter:
He probably knows a supplier.
The advantage of transflective technology is that it's not different from LCD technology. It just repositions some of the various layers to allow for the LCD to be visible without the backlight turned on. The disadvantage is that when it's viewed in low light conditions, the colors appear washed out. In fact, that was the reason the technology didn't see wide adoption. Corporations didn't think consumers would like it.