I think the ability to retrieve and display data in <20ms, thereby leading to interactions that are instant is still an open and underexplored UX issue.

What if you could just hover a link and all the important data would just appear?

What if you started typing a command in console, and the execution results would appear speculatively as soon as you hit the key?

Some programs do this to some limited degree, but besides the humble textbox and outside videogames, instant interactivity is seldom seen.