Any future Amiga would have to be backward compatible...Most of the good software was written for the 1.1-1.3 Kickstart. It should not be hard to include both ROMs and allow switching similar to a C128.
We also need to go back to blue, white, black and orange. It might just be me but I don't like the grey colors of newer Amiga OS. Interestingly, I noticed MS Office is using the old colors in Word if I remember correctly watching the GF type something looked at first like an Amiga...
Speaking of, the back and front gadgets need to come back to any new Workbench, handling Windows without them can be annoying. I really liked them to organize windows and not having to cycle through them.
But of course any new Amiga would also need new modular (so they can be upgraded) custom chips that can run applications (especially graphics) much faster than a PC or Mac (*shudder*). A built in TV tuner and interface, adjustable resolution that allows it to be used with either a TV or VGA monitor, hard disk and improved expansion ports for speed and self-configuration.