Hi Rikki
The changes in style formats that you mention is not new to Wersi owners, as when OAS 5 was introduced none of the styles could be played correctly on earlier versions. (Also earlier styles had to be converted (Facilities that were included within OAS 5) to play correctly on OAS 5)
When the OAA was introduced this also had a completely new format that cannot even be recognised by standard OAS instruments. (Not even OAS 7)
As to the Major Minor chord sets you mention, from how I understand it reading the manuals, the OAA has 16 sets for each part of the style (Currently up to 18) i.e. each fill, break, variation etc (Part) can have their own setup, and can be edited using the style edit functions onboard, (It also gives greater control when converting Midi files to styles)
Still, so long as arranger technology moves forward it can only be a good thing.
Regarding converting the latest PA800 styles then this also applies to Wersi which also cannot convert them; however we are promised that it will be implemented in the not too distant future. (The Wersi style converter, like the Korg style converter is based on EMC Styleworks, and so the conversions should also become generally available)
The future looks bright

Bill