Bluetooth module RN-42 support was integrated into firmware and hardware design was finalized now. Yes, it works well as Bluetooth keyboard for my usage at least. But due to limitation of the modlue it was not possible to realize all of what I expected, in particular battery life and connectoin switching.(I might be wrong but I won't pursuit any more.) Firmware is not final, I'm sure I'll update the firmware for usability and tuning.
Probably price will be $70-80(not includes battery), yes it is ridiculous.
Think again, you really need Bluetooth? You are welcome if you change your order to USB controller. PM me.
I'll contact some of you who are on wait list for BT controller.
Ask if you have any questons.
Inside and backside look like this. Not slick as consumer products.
You may want to make cover and knob yourself.
 
 
Capabitlities:      
- USB keyboard functions
    completely equivarent to USB controller including mouse keys and NKRO.
- Switching between USB and Bluetooth
    You can switch the two connections with BT switch or key combination.
- RN-42 config mode 
    You can change power/connection configuration of the module if needed.
- Low battery alert 
    Red LED turns on when low voltage.
- RN-42 status indicator
    LED indicates status of Bluetooth connection.
- Pairing           
    The module stores up to 8 connections.
- Auto connect      
    The module connects the last connected device automatically.
- iOS support       
    works as keyboard with iPhone5. No tested completely.
- Android support   
    works as keyboard and mouse with Nexus5. No tested completely.
- Mouse keys over BT
    Note that iOS doesn't accept mouse device.
- Battery charge
    You can charge from USB port or power adapter which has USB outlet.
Limitations:            
- Short battery life    
    Around 12hr with 1000mAh
- No connection switching
    RN-42 auto-connects to the last connected device.
    Some of consumer products can switch between devices, for example Logitech K480.        
http://www.logitech.com/en-us/product/multi-device-keyboard-k480?crid=26- HHKB JP requires case modification
    You need to drill holes for power switch and LEDs.
NOTE:                  
- 
Lipo battery is not included. Cannot ship it from Japan due to regulations. See 
this post for the detail.
- 
LIPO BATTERY IS VERY DANGEROUS, TAKE EXTRA CARE OF YOUR SAFETY AND PROPERTY. You can learn 
here.
- No NKRO over Bluetooth
- Check your country's wireless regulations and certification of the module.
RN-42 specification, documenations and certifications:
http://www.microchip.com/wwwproducts/Devices.aspx?product=RN42You can access files of PCB desgin and firmware here. 
https://github.com/tmk/HHKB_controller/ [PCB]
https://github.com/tmk/tmk_keyboard/tree/master/keyboard/hhkb/rn42 [Firmware]