Yeah almost there, but that's 2 devices...
Nope, exactly what you said we would have in 10 years. Just not 25". Phone goes into tablet, you have a tablet. Tablet into keyboard dock, you have a netbook/notebook. All run by the phone. If Asus is smart they will partner or just produce a TV that can dock the phone and get in to the Roku marketspace.
I did see a video form CES this year where the phone docking setup was hooked up to a 42" TV.
Might be ubiquitous tech in 10 or less years. It starts here.