It's an area not yet talked about -
Will this Tablet have a dock connector?
Is it to be used independently/docked to a Mac, or can it be used to dock a iPhone/Touch to?
Dependent on the OS this has different effects. I'd say it'll likely be some kind of larger iPhone OS - and it may well not have a 32 dock connector.
(What if they had LightPeak ready for v1/ v2 (I'd imagine a refresh cycle more akin to the MacBooks than the ATV, MAcBook Air etc
(And the tablet also begs the question - what happens to the MacBook Air - is the TAblet is a MacTablet Air type thing?))
In terms of accessories, I think if they're doing medical stuff - they'll have had to do FDA approval, or at the very least have designed it to be hospital compatible,and have to run the licensing and authorising of such a device in the medical workplace.
This event - the Tablet launch, iPhone v4, is likely why we haven't seen the wireless/wired medical accessories yet - They'll get launched together.
(There is I feel a backlog of accessories - I think Apple's been putting these on hold till the Tablet/ 4G iPhone/Touch).
Going along Ihnatko's lines, don't expect BT to do much. the quote is in the 5W thread in this forum, but basically, they want you to use the hardware they gave. They don't want keyboards, mice attached to iPhones , and that'll hold to an extent with Tablets (Unless they have a iMac like aluminium docking station...)
Beyond that? ANT+, medical wireless things - iTunes X will likely bring wireless syncing, we'll likely see a Front Row/iTunes change (with moves towards a Web based front end to iTunes (see the Apple KeyChest moves against DECE etc)...
There's a difference to what APple wants for accessories and what people want. Sure some will want to hack it. Most will go with authorised accessories - The majority of folks will be getting the products of the ever so secretive Made for iPhone and Works for iPod group (Which will now be the "Made for iPhone & Tablet and works for iPod" group?
Covers, hard shells, laminate covers for the screen for anti-smudges (though the oleophobic cover on the iPhone will come to the iTablet in all likelihood). If it has USB3, then you've got all those things.
It comes down to what OS this thing will have.