I appreciate the technical rigor required to make this kind of service stable and safe, but I am worried about the usefulness of the product / who would use it. Building APIs into my own abstractions in a real web application basically means I'll never use this myself. A more casual developer may use this to build simple mashups, or maybe hack out something for a hackathon, but beyond that why would I go through the trouble of figuring out how to integrate webshell with my own codebase? NinetyNine already mentioned this, but now I'm adding a new single point of failure and another web request, so I'm not quite sure how big the benefit is exactly.

Maybe it'll turn out that there's a huge need for some intermediate between IFTTT and vanilla API use, but I'm having a hard time seeing when.