I love AROS, but I have a hard time pinning my hopes on it, it's just glacially slow to progress.
Hyperion has the source and the ability to license, but tie to costly licensed hardware.
I could see MorphOS making a good run at Arm once the used Macs run out, but I don't think they are in too big of a hurry to make a new platform either.
Another platform shift would divide the few developers and users into even smaller groups than we have now.
Something like the Natami CPU is probably the better bet for Amiga long term IMHO.
When people think Amiga, they think 68k. All the beloved software is on 68k, the rest are almost always ports just because the 68k CPU was too slow.
Everyone seems to agree with 68k. If you don't have one, it's easy enough to emulate, so it has the most broad appeal to all groups.