From the above link, it sounds like with BB10, but there's no firm release date for that yet.
One slightly OT question I have is: can an attached device draw power from the PB usb port? So that, for example, I could run a mifi that doesn't include an internal battery? That would be interesting...
I'm not sure, but it probably is. The driver was discovered in previous versions by the Dingleberry crew, and IIRC they managed to enable it.
Originally Posted by Pokemon3DS
And obviously this means that you can use external memory on the Playbook
No, you can't. Feel free to try, but the functionality is either a) removed from the software or b) simply not enabled. It would be cool, but unfortunately can't be used at this moment in time.