Let's get this straight before we break our brains any further. A theory equals a theory. ID and evolution are actually on equal footing since they are both theories that are plausible. To say that ID is not plausible is simply closed minded. I am willing to accept that Evolution might be right, and that does not change my religious opinions. Can you say the same about ID?
No. A theory becomes a theory from the hypothesis after many facts are analyzed to support the theory. ID has no supporting facts.
What hypothetical observation would falsify the "theory" of ID?
A theory in science is not the same thing as a theory in common usage. Theories are the apex of scientific findings. This is why Relativity is still a theory. A theory is a scientific framework consistent with the evidence that scientists can use for making predictions or for directing research.
Except that ID is not a theory because it makes no predictions that would allow falsification. ID makes no predictions that would distinguish itself from evolutionary theory.