> So if I understand correctly then, the JavaScriptCore engine currently used in Webkit
> has two versions. One for x86/64/arm that JIT compiles the JS and another for PPC
> et al that is purely an interpreter?

Yes. You can read more from Fab there:

http://amigaworld.net/modules/newbb/viewtopic.php?topic_id=37255&forum=46#697350
http://amigaworld.net/modules/newbb/viewtopic.php?topic_id=37255&forum=46#697354

> Or is there just one engine and it also JITs for PPC too?

No.

> If the former, what happens if/when Webkit drops their interpreter?

Given that they quite recently changed their interpreter to a new one, I don't think they'll drop it.