1. 5V
2. I2C Data
3. I2C Clock
4. GND
5. I2S Clock
6. I2S Word Select
7. I2S Data
8. GND
9. SWD Clock
10. SWD Data
11. 5V

This was laid out so that:

• there was less chance of something being damaged if the ribbon cable was soldered/inserted backwards,
• communication, audio and debug pins are exposed, and
• clocks are next to ground pins to reduce crosstalk. 
  • I looked into Word Select and it seems to be either high or low for many clock cycles, so that's why I've put it in-between the I2S clock and Data.

I believe 1mm pitch would be the best ribbon cable to use, and an 11P one should be 12mm which should be the same as the expected length of the PCB (similar to the Tetrinsic PCB I designed last year, but its cable was on its width).

I'm going to rely on the internal antenna of the MS51SF1 for the time being, since similarly sized Bluetooth dongles and earbuds seem to have decent reception despite their small size. Thus, I haven't added an antenna pin to the pinout.