I was curious about just temperature.
From this pdf[1] it seems fingers have 3-5 cold sensing points per square cm, with cold sensing points being about 10x as prevalent as warm sensing points.
So I was thinking about using a combination of a thermoelectric cooler[2] coupled to some thin metal rods, which have individually wound coils around them near the top. The rods would be mounted flush to allow touching all of them at once. The cooler would ensure the rods are normally cold, and the coils would provide induction heating.
Thus by changing which coils are activated, the different rods would be either cold or not, and due to the active cooling and relatively low thermal mass should change state quite quickly. At least that's the idea.
Though perhaps we just don't have enough sensitivity in our fingers to pick this up. And it wouldn't work well for a portable device due to power draw.
edit: Found this[4] paper where they try a temporal method instead of spatial method to use temperature to convey information.
[1]: https://web.as.uky.edu/Biology/faculty/cooper/bio350/Bio350%...
[2]: https://en.wikipedia.org/wiki/Thermoelectric_cooling
[3]: https://en.wikipedia.org/wiki/Induction_heating
[4]: https://www.mdpi.com/2306-5354/10/10/1156