It does change the miner controller-scape only as far as the manufacturers are willing to embrace it. Bitmain walked away from the ar9331 modules (which would have cost them about the same) to the BB which, with their volumes, costs them about the same.
The Pi ZERO, though, is quite limited in terms of connectivity, aka ethernet and / or wifi, without further spending on enabling it, thus the $5 would end up being more like $15+ in medium volumes, even $30+ in small volumes. I can not see it below $10 with the connectivity added (to say the conrol board).
That said, the Pi ZERO will only change the controller-scape if an independent developer can fashion a drop in replacement controller board that it can host but most importantly, can run bitmain boards.
Some miners like Avalon have a chance as it's close to B/B+ number's. They use RPI as controller, so I would disagree with just independent devloper can use RPI's.
I do agree bitmain will not work due to using custom controllers. I still hope one day they switch over to RPI's. But it seems unlikely at this point they will ever do that.