Make the terminal very simple and easy to understand.
Rid us of the text-only terminal baggage that we deal with today. Even graphics are encoded as text, sent to the terminal, then decoded and dealt with.
Plan9 had the terminal right. It wasn't really a terminal, it was just a window which had a text prompt by default. It could run (and display!) graphical applications just as easily as textual applications.
If you want a terminal of the future, stop embracing terminals of the past.