I can't wait to get my hands on the stand-alone version that's supposedly on the way. Cheap and available (and compatible) hardware with decent performance is a long-awaited thing for a lot of Amiga enthusiasts.
If you want the most modern AmigaOS to run on classic hardware that's obviously 3.9 which was released in 2000.
https://en.wikibooks.org/wiki/Aros/Platforms/68k_support
(AROS is an AmigaOS open source clone. Source compatible for all other platforms, such as Intel, binary compatible for 68000.)
[0] http://forum.apollo-accelerators.com/viewtopic.php?f=9&t=190...