The decision to not support Fastboot was reached due to the following reasons:
The Texas Instruments BeagleBoard-xM BSP's u-boot doesn't support Fastboot or writing to eMMC
Back-porting Fastboot and eMMC write features to our u-boot version is non trivial
The b2g's Recovery Console is feature rich and supports brltty and thus is very accessible. A hypothetical Fastboot implementation on the b2g would not be very accessible.
If the recovery gets corrupted we can still recover using a bootable SD card or with the u-boot serial console. Therefore Fastboot is not mandatory.
The decision to not support Fastboot was reached due to the following reasons: