Unless SAGA hits multiple platforms on these new gen Amiga's besides the Natami, I don't see it getting much use. If such things are limited to just the newer FPGA Amiga's, there's really a limited market.
I doubt we will see much that bangs the hardware in the old fashioned sense, we are probably a decade to late for that to be much of a success. But I do expect SAGA to get a lot of easily converted opensource ports from linux and windows, blender, browsers, various emulators etc.
If these SAGA machines are a decent price, and speed, I could quite happily use one for web browsing and art programs again, and the odd game of quake2 and 3 would not go amiss either.
Having a modern machine, without having bits of hardware hanging off my Amiga would be nice, and if the demo scene gets on board, i'll be even happier.
I have the sneaking suspicion that NatAmi is going to be very expensive though.