First, I second the motion, James. Do it. It's not that the rest of us can't. It's just that the rest of us love your honest, often befuddled, and always informative approach. Get to it!
Ken Wrote
I think it would be a lot better to focus on individual varietals that can work on their own to make good espressos, and to vary these by season and by crop
I agree, because this is what I do... but I take this approach whether it is a seasonal blend or a Single Origin. Some coffees work wonderfully all by themselves as espresso and others need the support of a few friends. Much of what we do is both because we are small and repetition of flavor bores me. We change our espresso, on average, once every week and a half. There are hundreds of small farms producing wonderful coffee season after season. What better way to experience a larger palette of flavors than to be constantly changing?
Can all coffees work as SO espresso? Possibly. We just may not have the current skill set needed to capture their essence and bring it to the cup. Also, it depends if we are talking straight espresso or macchiatto/cappuccino. James used a wonderful Kenya during his WBC performance, which was probably too intense as a straight espresso, but something magical happened when in the cappuccino.
I think what we should ask is, "What are you trying to say with THAT espresso?" Maybe you want balance, maybe you don't. A shot mango and meyer lemon espresso would not disappoint me. Maybe you want chocolate and caramel, maybe you want in-your-face tart cherry. Maybe it's only for espresso. Maybe it's meant for milk drinks, or maybe, as in most cases, it's for both.
Another issue that some may want to take into consideration is that when we roast an espresso, it for what's best on our equipment in our environment, and while this may translate to your equipment and environment, to expect it to be the same is foolish. A competent barista working with an ECM Giotto and a Baratza Vario is still worlds different than the same barista using a Mirage and a Robur. And the gap widens further when on a daily basis the average home-barista, even with great equipment, may make a few espresso, rather than few hundred.
Single Origin or Blend... It just has to be good.
Espresso. There are no simple answers.