I had the same idea...;)...mainly regarding propper support of X5000 (non-Altivec).
...but was unfortunately told, that there is not so much benefit from the OS4 version. So, obviously, there would be big mountain of work...
But, maybe, if other users also "insist"...? :)
AmigaOne X5000 @ 2GHz / 4GB RAM / Radeon X1650 / AmigaOS 4.1 Final Edition / MorphOS 3.17
Amiga1200 / Blizzard 1230 IV PiStorm32-lite / 128 MB RAM / AmigaOS 3.9