This is why the API should ALWAYS at least have a first pass before any coding is done. Changing how things look and feel after the fact? Not an issue. Changing the underlying data structures? Holy shit, kill me now. Hell, if your API is solid (and you're using actual restful calls) then you should be able to completely decouple UI coding, business logic, and data management. Of course with the modern love of AGILE (see rapid prototyping) people wonder why so much rework is always needed because that's simply not the case.