The support question is really interesting. If Google is the company that takes the money, they will be the company that people would expect to handle refunds, returns and general support. Unless Google is planning something new, there's no way that they are geared to deal with the barrage of consumer support issues that will appear.

I don't see why the majority of online resellers would be concerned by being "reduced" to "back-end order takers". That's the easy part of the business, while payment and customer support is the expensive and annoying part. Most consumers are not loyal to any one online reseller anymore, Amazon excluded perhaps.

If I was to pick where I would want to be in terms of online retail in the future, I would want to be the business with the warehouse and just supply eBay, Amazon, Google and any direct shipping customer I could find. That's where the money is in the future, at least that's what I believe.