In a more limited market one could probably do whatever because with little competition your audience is captive. Whether many of them would "get it" remains to be seen.
Great topic and one I have wondered about for some time.
I would think it would help to be consistent with a couple roasters at least and maybe feature a new micro-roaster every month. I don't know, but that seems like it would be a middle ground to serving your customers something they love or can depend on while trying something new. Maybe?
It's a small but thriving shop in Atlanta called Rev Coffee. They're doing coffees from Batdorf, Intelligentsia, and 1000 Faces (based out of Athens, GA). They usually stick with Intelly's Black Cat for espresso, some sort of "house blend" always, and rotate out a SO offering (today it's a Rwandan).
When I've had conversations with different people within the industry, it seems like the consensus (at least in the past) was a leaning toward exclusive relationships. I agree that if you shoot for an identity of "quality, choice, and educational possibility rather than around one individual roasters", then having a "diverse" shelf makes sense. But are there certain advantages of a singular affiliation that simply make for good business? Where the masses possibly won't care as much about who you're offering, would you maybe benefit from those who would gravitate toward your place out of brand loyalty? For example, I know of many Counter Culture fans who go to Octane in Atlanta just because of that relationship. Is it a possibility that some of that business might be lost if Counter Culture were simply just another name on the shelf or chalkboard?
I ask these questions mainly because I'm debating on what to do with a shop I'll be in charge of in the near future. I want to make a decision that makes good sense from both a coffee steward and a business point of view. Personally, I've enjoyed dedicated relationships with roasters in the past and would hesitate to sacrifice that, but I'm open to the idea of multiple roasters.