Talking about non-Disney vendors in WDW, keep in mind that at the time MickeyD's was brought in, Disney had a really bad rap for the quality of their food. MickeyD's gave WDW an internationally recognised, unquestionably American restaurant functionality with a reputation for consistancy. Mickey D's is also widely popular with kids and the folx at the _other_ end of the human life cycle, and is someplace that people would go to. Disney killed two stones with one bird by partnering with Mickey D's.
Adding a name brand coffee house might not serve much of a purpose in WDW. Other than Seattle and the Pac. NW, no one really worries overly much about coffee reputations. If adding a chain to a DVC resort will materially lower the maintenance costs and not ruin the atmosphere of the resort, I'd say go for it.
Just a few java thoughts...(no, not the computer scripting language, the drink).
1) I'm not sure if the Poly sells the coffee they brew, but Kona and other 'premium' coffees are staples at most coffee selling houses. If you don't have one near you or if they don't carry the 'premium' beans, I'm sure you can always find someplace on the 'Net to mail order them. Just be sure that any thing like a Kona is 100% Kona beans. They're alot of 'blends' out there where they can throw 1 bean in and call it 'kona' blend.
2) Kona, Jamaican Blue Mountain et al are "expensive" to buy. Around Philly Kona runs in the $30-35/lb range. JBM was selling nearer to $60/lb, though I've just seen it for $35 at the Reading Terminal Market in Philly.
3) In reference to item #2, if you think the price is high, consider how much otherwise 'frugal' people spend on a cup of coffee at a coffee house.
4) DVC rooms all have coffee makers, and packing a grinder or getting freshly ground coffee for a trip is the most frugal way to drink premium coffee.
5) Supermarket 'premium' coffee is generally better than the stuff you buy in cans from the mass producers, but not always.
6) Fresh Ground (esp. with a burr grinder, like the coffee houses tend to use) is almost always better.
7) The water and cleanliness of the brewing mechanism is as big a part of getting a good cup of coffee as the coffee itself. Since so many people seem to have issues with the Floridian water, bringing a filter or buying bottled water for coffee might help.
8) If you like adding things like chocolate or other flavored syrups, does it really matter what the underlying coffee is?
9) Rum cream (similar to Irish cream) makes a wonderful creamer replacement for the days when you don't have to worry about the fact you're drinking booze before you leave the house.
10) Don't be skimpy with the ground coffee for brewing. Trying to run too much water through too few grounds will probably make bitter coffee. If you need 'weaker' coffee, water it down in your cup. I keep trying to tell my in-laws that they can always weaken their coffees, I can't strenghten mine.
Hope this helps,
Joe - coffee gourmand