It just isn't gonna happen, Hyperion have invested a lot of time into this project, 4 years as a matter of fact. That costs a lot of money in terms of paying a few programmers (and yes there are a lot of part time volunteers)
AmigaOS requires devotion, and personally I am glad it's not available public domain so that people can get hold of it and modify it etc. we need a stable OS that doesn't need constant recompiling etc. Besides, I would like to be able to go into a shop one day (Pipe dream I know) and buy an Amiga title etc.
Unlike other open OS's where one person buys the product and the rest just pirate it.
I guess, we'll have to agree on disagree, I don't think making AmigaOS open source would take it any further to be honest.