[groone]

I think they would rather leave some USB port available than let you wear down their chains

[mytailorisrich]

More likely that they'll upgrade the bikes to lock the chain/pedals if this becomes a problem.

[uoaei]

Considering there's negligible tension on the chain when pedalling backwards it's not really going to have much of an effect. And the added gear ("jockey/pulley wheel") is plastic.