But I have definitely read elsewhere that autocorrect would support bluetooth/external keyboards
I see some sites say external bluetooth keyboards, while others say software keyboards, which are not the same thing. I cannot find anything directly from Apple, so I have no idea what the truth is. The closest I could find was from the WWDC keynote video, where it says on the screen near the end, "Autocorrection for every keyboard". You would think that would mean Bluetooth, but who knows?
I posted on the Apple Support forums, so we'll see what they say there.