I just read the thread. We already have two hdl implementations of the AGA chipset, mine and the minimig derived one. We have extensions such as extra memory, RTG, AHI audio etc already.
I guess the game here is to add propriety extra features and build a new platform, but that potentially breaks back compatibility. For them it makes sense to open source that part of the design to encourage people to use those features. Personally I'm much more interested in a new, cycle accurate (and high performance compatible) open source CPU, which is what we are working towards.
Why not just compile AROS to cheap modern CPU platforms?
/Mike