TESTERS AND TEST PROGRAMS:
As processes shrink (see Moore's law), the leakage current becomes much higher and less predictable. This makes it difficult to tell a low leakage part with a defect from a naturally high leakage part.
Also, increasing circuit size means a single fault will have a lower percentage effect, making it harder for the test to detect.
However, Iddq is so useful that designers are taking steps to keep it working. One particular technique that helps is power gating, where the entire power supply to each block can be switched off using a low leakage switch.
This allows each block to be tested individually or in combination, which makes the tests much easier when compared to testing the whole chip.