And who will do this and on what hardware? How will it get marketed?
The marketing is easy. Hire the experts. Bill Gates, more than anyone else in history, has demonstrated the power of good advertising. Marketing is best left to the professionals. Regardless of what it costs, a good marketing strategy is worth it. Sign up for the old platinum account at Ogilvy & Mather (or other top firm) shovel a truckload of cash into a "flood the airwaves" style marketing campaign, and you're set. You could be peddling total garbage (Like Gates) and it would still reap 7 figure sales. The public (especially American) have proved this time and again.
You ask on what hardware a new Amiga might run? I myself favor completely redesigned hardware made to look and "feel" like a classic Amiga -- not some stock, "me too" vanilla PPC board with an "Amiga" bios. A radical new design, something totally outside the box -- so much so that the it would be impossible for the inbread technology press to ignore it. I would seek a totally scaleable, modular design. Something you would instantly recognize as an Amiga (elegant, responsive, intuitive...ability to multitask instead of just make the claim, etc..), yet futuristic. Not "modern", but years ahead of its time, just like the classic Amiga was for the better half of the last two decades.
This is just how things would proceed if I was in charge.

I'm by no means "rich", but I do save, and have got a pretty tidy amount built up.. Plus a couple of well compensated friends... If indeed you see Amiga, Inc. go up for sale for, say, 5 or 10 grand? Maybe we'll see some movement.