I got a RaspberryPi recently and have been wondering what to do with it.
I'm kinda keen on doing something similar now ("Mirror Mirror on the wall... what's the forecast for this evening?"). I think the issues are going to be how to keep it as low profile as possible, and to reduce power consumption. There were a few suggestions of full size monitors to put behind a two way mirror in the comments, but those tend to be pretty thick and chew up quite a bit of power. Some of the modular displays for things like the Pi seem like a better idea, and having them tied to something like Jasper for activation, rather than being on all the time could further cut down on the usage.
The other appealing aspect of something like this is that it's not as intrusive as other digital assistant feedback. Siri, Alexa, Cortana, Google Now etc have voice feedback, but to be relatively hands-off you need to be able to hear their responses, and thus have the volume up. If it's something that you're looking at (shaving, brushing teeth, doing hair etc) but can just ask for information and have it be displayed just to you then it means you're not bothering anyone else with a fake personality telling you "Brr, it's cold outside", a la Siri, which is amusing at first, but annoying if you just want to know what to wear. Having it only activate on demand also means the rest of the time it's still something useful like a mirror but not displaying something you don't care about (as a computer screen, smart TV etc would).