They are interested in both, so how about a VR headset; what resolution would you recommend? I haven't the foggiest.
On a tablet, it's the idea that you stand somewhere and get a message that you can see what it looked like, say 1000 years ago; you hold the tablet in front of some house or area and see what it would have been like then, turning around you can see all, possibly partially blending in with reality (I told you he was vague). For that I think some 2000px (no stereo of course) would be enough.