I think a screen would add a lot of functionality. It could display music info, show you options when ordering something, show recipes, etc. For me, the biggest drawback of the Echo is when I need to go into the app for more info, so I think that this would solve that and make it much more useful. Still, this doesn't solve my other main complaint about the Echo, it needs high quality stereo speakers. Listening to music is fine and all, but I still go to my Sonos for better quality.
Looking forward to Apples half-ass attempt at a competitor.