AmigaOS 4.2 will incorporate AmigaDE so there's no need to mess with OpenAmiga. BTW Amiga OS 5 is supposed to be portable to any AmigaDE supported platform when it shows up. The generation 4.0 Amiga standard is just a work in progress leading up to a grand solution.
When AmigaOS 4.2 gets developed there won´t be any Amig Inc anymore and therefor no DE. DE doesn´t have anything todo with real Amigas anyway.
I suppose that in the future it will easiest to develop on a completed AROS for the OpenAmiga standard and then port to the other platforms.
Otherwise we are stuck in WB 3.1 :-(