Largely in agreement with KennyR's last post, but I would add to it that the open source movement has revitalised the software industry which was very much in stagnation.
A variety of opensource and commercial software is what's needed. The advantage of OS4 being commercially-based is that its development will be much quicker than if it were opensource, unless all opensource developers everywhere for some random reason decided that OS4 was the "next big thing".
I think an opensource community developing anything for new Amiga platforms (A1/Peg) is a good thing. Even Linux. It gives the platform greater visibility to the techie community.