Well, from the looks of it, the hysteria seems to have subsided a bit, so let's hope we can have a civilised discussion now without that handful of loudmouths trying to shout it down.
It's funny you should bring up McDonald's. If ever there was a precedent for the $bux construction, it was Disney's contract with McD's of last decade.
McD's products, menu was introduced into the parks. Subtly, themed. Very much like they intend to do with $bux. But it was still a theme breaker to me. A breaking of the fourth wall. The addition of McDonald's' industrially perfect fries wasn't an addition to me. It was a distraction. McDonald's is what you want to leave behind you, in the real world. I didn't need to have the world's 19,873th McDonald's counter in the MK.
There is a subtle but important difference between Coke, Edy's and Nescafé's presence in the parks, and that of McDonald's or Starbucks. The former are tangible products, the latter are physical spaces, places one visits. It is fine for WDW to serve Heinz Ketchup with your fries, but not to order those fries from a McDonald's menu.
I was happy to see McDonald's leave the parks again, and I hope Starbucks will soon follow suit. It felt intrusive, as Starbucks will feel too. Even though I do expect the lines to run all the way to the Train Station.
The 'Refreshment Port featuring McDonald's favorites' in EPCOT:
The themed McDonald's cart in FL:
Further reading:
http://www.yesterland.com/mcwdw.html