Imagine Sailfish phone other half lets you hook it up to a vidock and play steam games.
That would be awesome.

DUDE! This is very very possible!

OtherHalf thats goes all around the phone with:
-extra memory for games (gameboy cartridges?!)
-mega giga battery
-cooling of the phone!!!!
-gamepad buttons

I would totally like this

It would be pretty cool if custom OHs also incorporated pogo connectors. The Nexus 10 has them, and they allow for quick charging when you have a dock with the Magnector built in. Some guy on XDA sells them, but you can mod a Toshiba tablet dock to fit, or build your own.
Pogo connector:


Magnector cable:


Modded dock:


xda thread

The only thing I would need in TOH is a stylus holder.

Other nerdy OH ideas there: https://www.tindie.com/products/category/sensors/

A good capacitive stylus + holder would be cool, I agree, especially if we inherit some apps like EasyDebian and stuff like that. I'd buy one.

This looks pretty awesome

http://www.engadget.com/2013/12/06/l...case-hands-on/

Probably this has been mentioned, but if If I2C is too slow in bandwidth for some application that would require USB speeds, then why not let:
1. Other half connect with a tiny cross-over in the phone usb port (then you have the possibility for camera speeds etc in host mode with special driver). It might look a little funny though.
2. Since connection above take away the USB port on the phone, then provide a new USB port on TOH itself to become that regular USB-port that you connect to say computer or whatever.

Does this make sense?
Power-issues, to let the jolla power both ports, I haven't though of. But I guess other half also could provide some of the extra juice needed for the additional USB port by a power source itself.

A good example where the I2C would allow to drive it directly from the camera app with small changes.

Doing this is possible, but it would requiere a USB-Hub chip in the other half, to provide 2 ports : one for connecting to the other half device, and the second one to recover the phone port.
However, doing so, I think the phone can only be in host mode, not in device (so you couldn't connect it to a PC). Not sure about this, this as to be checked.

It has to be done carefully, but should be possible. It depends on how the internal power system is done in the Jolla (not info on this yet), and what you want to do through this port: charging the phone, powering an external device, ...