How will that change anything?

It will cost as much as an Nvidia 1080 and probably only slightly faster than the current 390/480, which nobody will buy unless ZEC/ETH skyrocket in value sometime in the next few months.

You make it seem like VEGA = Some ETHEREUM ASIC, which is the only thing which would destroy ETH.

If the VEGA was very cheap or free, then yes "IT WOULD DESTROY ETH".