Just to clarify a few points:
1. Arexx is not dropped from OS 4.0, it is included "as is".
That's the reason it was not mentioned in the document.
(Note that the source-code is almost entirely in 68K ASM and we doubt it is legally even possible to port it to PPC. We are working on a replacement WITHOUT DROPPING AREXX)
2. Some people seem to have misinterpreted the part in the description of the memory handling related to AGA.
This means that it will be possible to "fake" the presence of chipmem on systems without chipmem so that more legacy applications will work.
It does not mean that AGA is somehow "emulated".