Booting - User device selection in U-Boot?

[khanku]

U-Boot selectable device target:
        - Pause & blink LED, (which one?), for a short time, (5 seconds?)
        - During this time, accept keyboard input
        - Select boot device of:
                - eMMC, (number 1?)
                - MicroSD card, (number 2?)
        - Timeout default using current scheme, MicroSD if installed, eMMC otherwise.

This reminds me of how Qi used to work on OpenMoko phones. While not quite convenient it was functional and would certainly be an improvement on the current u-boot situation on the pinebook pro.