You can add ethernet to the Pi ZERO by simply plugging in a mini USB to ethernet dongle which costs about $10. But the cost difference between a BB and a Pi ZERO is not even that (reportedly the BB costs bitmain $7) and both will require a daughter-board (even for Avalon).

That is the reason I said the Pi ZERO will not be of interest to Bitmaintech, however, for an independent developer, there definitely is some scope. Technically on a simplistic level, it is merely a matter of serial interfacing with the hash boards which can be achieved with the Pi ZERO as much as it is with the BB.

With regard to bricking, for the S1 and S3 that was an issue in the ealy days, but unless there is damage to components, recovery from bricking is a breeze and aside from time, costs a meagre $3 for a USB to TTL dongle. Ofcourse with the BB, you can always pop down your favourite webstore for a replacement so bricking and time to RMA is moot.