I, too, am interested in this idea, and I think there are signs that the American public are interested in paying more for a quality product even as our pockets are emptier. We are tired of the crap we've been fed for so long, and perhaps look more to quality over quantity a bit more these days.
I know some of the farms here which sell fresh chicken to the public are using hybrids of their own design, and there are other farms making dual purpose or meat breeds that fit their ideals rather than taking what is out there. One example is the Copper Scotch.
I'm interested in my own projects, which fall under this purview, and have been working on a dual-purpose bird with a cushion comb for a Winter-hardy forager and 2 meat seasons. This is a bird that has Chantecler and Orp blood along with a few others- it is huge but can find some of its own food while enjoying winter. The egg production is quite good. I'm still working it to breed true to a specific conformation.
Back to the flavor- I think that I've finally agreed there are varying qualities imparted by the forage, insects, and feed any particular bird is eating, but with that come natural qualities the bird possesses. The Chantecler is a bird which weighs significantly more than it appears to. It is a LEAN bird, with almost no fat, and has a wonderful delicate aromatic flavor, even at 22 weeks- and is very tender despite the age. If a normal grocery bird is 6-10 weeks old, it obviously costs more to get a bird to butchering size, but I haven't found too much difference in an 18 week-old Chantecler, so I think as this project progresses I'll be able to select for a 14-week ideal. I think it would be well worth it to have a fine bird at that lengthy growth. The Orps I'm using are massive and rather quick-growing, while I've considered throwing in some Marans, as I have a line of FBCM that grow so fast it's almost amusing. That would likely lend flavor from all accounts, though I can't say from personal experience.
I'd like to know what folks think of the flavor of various breeds, and I'm going to start a thread asking as much, after which I'll run a poll so folks can vote for the tastiest from the top 20 breeds named. Perhaps then I can do the same for various feeding practices/substances.