Features:
Aros:
I think the main advantages (between others) are that it is available for different hardware (X86, ARM, 68k and I think PPC) and even hosted (f.e. on Linux what is a nice option :-) ) and 3D support.
I try but I am no expert for AOS and MOS...
MorphOS:
MUI4
Ambient (or similar)
Poseidon (already in MorphOS and Aros)
and a lot more I do not know :-)
I don't know either! Iggy, Itix and TMHG, what are the MorphOS features/software that stand out for you?
AOS:
I do not know much about AOS to say any features because I do not use it. I know that there are many components done different like Reaction instead of MUI, another USB-Stack...
Off the top of my head, the (admittedly not-perfect) shared object suppport, Timberwolf and QT are the ones that spring to my mind. I really like QT once you get your head around its extra declarations in C++.
3.1.:
Most things you can do in 3.1. you already can do in any of the NG-platforms. I think main advantage is the huge software-base, so tons of software :-)
Absolutely agree, so that implies 68k (and for games I would love AGA) emulation is really important.
What I think what should be there:
common drivers (USB, PCI)
cross-platform support (including hosted versions)
cross-plattform development tools
common software
API should be equal (as far as possible), GUI can be different (like KDE or Gnome)
Yup when you've used eclipse or visual c, it shows how our development tools are lacking. Even though I often stick with a test editor and a sheel, an easy to use debugger, etc. are worth their wait in gold. I use SAS/C on the 68k side, Codeblocks/Eclipse for Linux too. I know that OS4 has codebench, what are the options on MorphOS/AROS? I'm guessing they're gcc- and vbcc-based too?
But yes commonality across the API and for drivers can only be a good thing.