Nicely done. I like what they did with the programming port too! But I'm just as wary of the battery life as anyone who's seen these mods before.
I don't think Bluetooth is the problem, power consumption wise. It's the USB step in the middle, with all that "bitbanging" the Arduino has to do, at high speed without sleep, against the HHKB's own controller. Well, unless I'm forgetting where the controller resides again, which I'm sure I have done for something like this before!
Talking to Xwhatsit about capsense controllers in general, he reckons there's nothing inherently more power hungry about them than an Ohmic (non capsense) controller strobing a matrix full of diodes. His Model F and Beamspring controllers aren't optimised for power consumption, as like the HHKB they run on USB anyway. But he reckons a replacement wireless controller for capsense boards like the HHKB and other Topres / IBMs could have good battery life if designed around that goal from the outset.
I'm an HHKB short of being able to pursue this myself. But the SSK looks like an
excellent candidate for a replacement Bluetooth native controller. I'd like to have a built in USB controller as well, as backup for running the keyboard in a Bluetooth unfriendly environment, and more importantly for programming the Bluetooth controller if it has no USB. A USB port is essential anyway for conveniently charging the battery. Hell, I'd even pop a hub in there if the keyboard shell had a nice spot for it! Wireless and wired use cases are very different.