>Warning...may cause significant flaming (I hope not)<
I think it kinda depends on exactly what you see amiga as. For me, Aros as a rewrite of os3.x, counts. And given the advances the Aros team has made, I don't think there is any reason Aros can't be a perfectly usable desktop os in just a few years time.
The biggest difference between Aros, Morphos, and OS4 is the same difference between a modern pc and a PPC amiga. Aros has access to gigabytes of ram, Gigahertz multicore cpus etc. etc. for CHEAP.
Aros needs full Web capability, more media capability, and more apps and games and it is good to go. And as it is based directly on os3.x I would say that Amiga is capable of being very fully modern.