I believe Hyperion owns the rights to OS4.0+ but Amiga Inc still has 3.1 so could do it if they wanted to.
I think it could be breach against Amiga Inc/Hyperion settlement so I dont find it likely Amiga Inc could open source it. On the other hand I dont see Hyperion has rights to open source 3.1 because they dont have enough rights to it (only to modify, sell etc).
You could always ask from Hyperion's lawyer, Ben Hermans.
