Personally, I think it's reasonable for a small 1-2 person shop, but if you are planning a larger company it's pretty irresponsible to build it around someone's

Personally, I think it's reasonable for a small 1-2 person shop, but if you are planning a larger company it's pretty irresponsible to build it around someone's API like this. If you can't feasibly replace a given API, then you're business is incredibly fragile, and I think it's unfair to employ a large number of people in a fragile business without clearly stating to them that they could all be unemployed in an instant.