what about Arexx in OS4 ?

[Rogue]

Yes, AREXX is going to be replaced - or rather, AREXX will stay in its current form, and a new scripting language will be brought in.

This is not only because of ownership considerations. There are other things, mostly the fact that the AREXX implementation is very sensitive with its internal data structures which are accessed by some function located in linker libraries - meaning that any change in internal structures will break the whole thing.

As such, AREXX will stay for backwards compatibility but people are encouraged to use something new - most likely Python, but we are looking at other alternatives.

[Rogue]

Would it not have been possible to take a similar approach, and present the original ARexx runtime to emulated applications, and (for example) a regina based runtime to PPC applications? (I'm not saying thats what you should have done; just curious)

The major problem with AREXX is the way that internal data structures are handled. The interpretation of the commands itself isn't a problem. Bringing in Regina only takes care of the pure interpretation of commands. It doesn't solve the way that the interprocess communication works.